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JJlilYERSITY   OF   CALIFORNIA. 

BERXELEYN,  

.IBRARY 

INIVERSITY  OFi 
CALIFORNIA 


r         , 

yk. 


FROM   THE    LIBRARY   OF 

JOSEPH  LECONTE. 


5C 

.IBRAF  i 


GIFT  OF  MRS.   LECONTE. 

No. 


EARTHQUAKES,   VOLCANOES, 


AND 


MOUNTAIN-BUILDING. 


THREE  ARTICLES  PUBLISHED  IN  THE  NORTH  AMERICAN  REVIEW, 

1869-1871. 


BY  J.  D.  WHITNEY. 


UNIVERSITY   PRESS,    CAMBRIDGE 
1871. 


::•  '  .'I 

SCIENCES 
LI  BRA.:  Y 


CONTENTS. 


PAGES 

1-32 


EARTHQUAKES   .       .        •        •        -        • 

VOLCANOES    .        - •        .33-67 

VOL.CANISM  AND  MOUNTAIN-BUILDING     .       .        •        .  €9-107 


101436 


NOTE.  —  The  first  of  these  articles  appeared  in  the  North  American  Review  for 
April,  1869,  Vol.  CVIII.  page  578  ;  the  second,  July,  1869,  Vol.  CIX.  p.  231 ;  the 
third,  October,  1871,  Vol.  CXIII.  page  235.  A  few  extra  copies  of  each  were 
struck  off  and  are  here  placed  together  for  convenient  distribution  to  friends  and 
those  who  may  be  specially  interested  in  the  subject  of  volcanism. 

J.  D.  W. 

CAMBRIDGE,  October,  1871. 


EARTHQUAKES. 


1.  The  First  Principles  of  Observational  Seismology.      By  R. 
MALLET.    2  vols.    Royal  8vo.    London.    1862. 

2.  Untersuchungen  uber    das  PJidnomen    der  Erdbeben  in   der 
ScJiweiz.    Yon  G.  H.  OTTO  YOLGER.    3  Theile.    Gotha.  <  1857. 

3.  Volcanoes  and  Earthquakes.     By  MM.   ZUECHER  and  MAR- 
GOLLE\     8vo.     Philadelphia  and  London.     1869. 

THE  titles  placed  at  the  head  of  this  article  indicate  three  as 
characteristic  books  as  could  he  selected  from  among  the  mass 
of  publications  devoted  either  to  earthquakes  alone  or  to  earth- 
quakes and  volcanoes  conjointly.  In  the  last  one  on  the  list 
we  have  a  fair  specimen  of  a  class  of  books  which  are  becom- 
ing quite  common,  which  mostly  originate  in  France,  are  trans- 
lated in  England,  and  are  reprinted  here,  and  which,  while 
pretending  to  be  scientific,  are,  in  reality,  as  far  from  having 
any  claim  to  that  character  as  possible.  The  principle  on 
which  these  books  are  got  up  seems  to  be  this :  A  number  of 
showily  designed  and  elegantly  engraved  wood-cuts  are  manu- 
factured, and  then  some  scientific  penny-a-liner  is  hired  to 
put  together  a  text  to  match  the  pictures,  no  time  being  al- 
lowed for  doing  the  work  properly,  even  if  the  person  selected 
were  competent,  —  which  is  rarely  the  case,  —  the  dominat- 
ing idea  being,  evidently,  to  produce  something  which  a  not 
very  critical  public  shall  be  tempted  into  buying,  on  account  of 
the  beauty  of  its  mechanical  execution,  and  with  the  incidental 
advantage  of  getting  something  scientific  into  the  bargain. 

The  materials  for  the  illustrations  and  text  of  such  books 
are  taken  right  and  left  without  acknowledgment,  the  one  cari- 
catured and  the  other  "popularized,"  —  that  is  to  say,  enor- 
mously exaggerated  or  misrepresented,  partly  through  igno- 
rance, but  chiefly  through  a  desire  to  produce  a  sensational 
1 


2  Earthquakes. 

effect.  The  result  is  even  worse  than  that  produced  by  the 
modern  sensational  novel ;  for  the  latter  is  read,  thrown  away 
and  forgotten,  while  the  pseudo-scientific  and  elegantly  illus- 
trated volume  is  carefully  laid  away  in  the  book-case,  and 
referred  to  as  a  standard  authority,  and  most  certainly  added 
to  the  dead  weight  of  every  public  library,  crowding  out  that 
which  is  really  valuable  in  the  same  department,  and  which  is 
overlooked,  perhaps  because  it  is  a  little  old,  because  its  exte- 
rior is  not  attractive,  or  because  its  appearance  has  not  been 
heralded  by  a  publisher's  fanfare. 

There  could  not  be  a  better  instance  selected,  as  a  text  on 
which  to  preach  a  sermon,  a  propos  of  this  style  of  illustrated 
works,  than  that  furnished  us  by  this  book  of  MM.  Zurcher  and 
Margoll^,  whoever  they  may  be.  The  illustrations  are  showy, 
and,  as  far  as  the  engraving  is  concerned,  well  executed, 
though  badly  printed  in  the  English  edition  from  the  pur- 
chased electrotypes,  while,  in  the  original,  that  branch  of  the 
mechanical  execution  was  undoubtedly  carefully  attended  to. 
But  let  any  one  conversant  with  the  subject  of  which  the  vol- 
ume treats  examine  the  illustrations,  and  he  will  see  at  once 
that  the  drawings  were  made  by  persons  entirely  ignorant  of 
what  they  were  attempting  to  represent.  Thus,  in  the  views 
opposite  pages  10  and  34,  an  attempt  is  made  to  show  the 
phenomena  of  violent  eruptions  of  Etna  and  Vesuvius.  Now, 
if  there  is  any  characteristic  feature  of  these  eruptions,  it  is  the 
straightness  of  the  column  in  which  the  projected  material  as- 
cends until  it  reaches  its  highest  point.  In  these  drawings,  on 
the  contrary,  apparently  in  order  to  add  the  curve  of  beauty 
and  grace  to  the  picture,  the  column,  in  both  cases,  is  made  to 
ascend  in  an  elegantly  waving  line,  as  untrue  to  Nature  as  pos- 
sible. Again,  every  one  is  familiar  with  the  sketch  of  Cotopaxi, 
given  by  Humboldt,  as  an  illustration  of  a  beautifully  regular 
volcanic  cone,  and  which  has  figured  in  hundreds  of  books 
for  the  last  fifty  years,  —  notably  in  our  school  geographies. 
Humboldt,  in  his  sketch,  misled  by  the  invariable  tendency  of 
the  eye  to  exaggerate  the  slope  of  mountains,  represented  the 
inclination  of  the  sides  of  the  cone  as  48°,  while  the  photo- 
graphs show  that  in  reality  this  angle  is  no  more  than  28°  or 
29°,  the  greatest  inclination,  just  at  the  summit,  being  only  32°. 


Earthquakes.  3 

Now,  on  the  wood-cut  in  MM.  Zurcher  and  Margolle's  book, 
the  slope  of  all  the  snow-covered  part  of  the  volcano  is  given 
as  55°,  while  the  effect  of  the  whole  is  very  much  like  what  one 
might  imagine  would  be  produced  by  a  stove-funnel  perched 
on  the  summit  of  a  big  boulder.  This  is  the  character  of 
the  illustrations  throughout ;  there  is  one,  however,  which  sur- 
passes all  the  others  in  its  ludicrous  absurdity, — representing  a 
great  number  of  Calabrian  peasants  in  the  act  of  being  swal- 
lowed by  earthquake  chasms,  the  whole  style  of  the  thing  being 
well  suited  to  the  pages  of  a  comic  almanac,  perhaps,  but  cer- 
tainly not  to  those  of  a  scientific  work.  Of  the  text  of  this 
book  it  may  be  said,  without  hesitation,  that  it  is  fit  to  go  with 
the  illustrations.  Let  a  single  suggestion  be  quoted  from  it,  to 
show  how  that  which  is  unsound  in  theory,  but  at  the  same  time 
brilliant  and  peculiarly  French,  is  mixed  with  something  sup- 
posed to  be  popularly  and  economically  interesting,  —  the  idea 
being  to  convey  the  impression  that  science  has  its  practical 
as  well  as  its  abstruse  side.  M.  Elie  de  Beaumont,  a  distin- 
guished French  geologist,  has  devoted  much  time  to  tracing  out 
on  the  earth  a  regular  geometric  arrangement,  with  which  he 
thinks  the  lines  of  upheaval  of  mountain  chains  may  be  found 
to  coincide,  and  which  he  calls  "  a  pentagonal  network."  The 
idea  is  ingenious,  and  has  been  elaborately  wrought  out  by  its 
author,  but  accepted  by  few  of  the  leading  geologists  at  the 
present  day.  Our  authors,  however,  make  both  themselves 
and  the  pentagonal  network  ridiculous,  by  advising  that  it 
should  be  used  as  a  guide  in  boring  for  springs  of  petroleum. 
They  even  trace  an  imaginary  line  from  Iceland  straight  to 
Oil  Creek,  "  places  remarkable  for  their  bituminous  emana- 
tions," as  a  guide  to  "  oil  prospectors."  .  What  a  pity  this 
brilliant  idea  had  not  been  suggested  before  the  collapse  of 
the  great  bubble !  One  might  then  have  had  the  "  Great 
Consolidated  Pentagonal  Network  Petroleum  Company "  to 
add  to  the  list  of  other  remarkable  things  in  that  line. 
All  that  is  said  of  the  volcanoes  and  volcanic  rocks  of  our 
own  country  in  MM.  Zurcher  and  Margolin's  book  is  equally 
curious,  as  an  exhibition  of  entire  ignorance  of  our  geography 
and  geology.  There  are  just  about  as  many  misstatements  as 
there  are  lines  in  the  two  pages  devoted  to  North  American 
volcanoes. 


4  Earthquakes. 

Herr  Volger's  book  is  as  thoroughly  German  as  that  just 
noticed  is  French.  This  author,  living  at  a  distance  from  any 
region  of  volcanoes  and  great  earthquakes,  but  in  pne  where 
moderate  shocks  are  frequent,  and  having  a  strong  propensity 
to  look  at  natural  phenomena  in  what  may  be  called  "  the  small 
way,"  has  evolved  a  theory  of  earthquakes  from  the  depths  of  his 
moral  consciousness,  and  then  endeavored  to  bolster  it  up  by 
collecting  great  numbers  of  facts,  also  of  the  small  kind, 
entirely  ignoring  the  greater  facts,  to  which  his  smaller  ones 
are  as  the  ripple  on  the  surface  of  the  ocean  in  a  gentle  breeze 
to  the  great  tidal  wave  which  encircles  the  whole  globe  in  its 
motion,  and  stirs  the  waters  to  the  very  profoundest  depths. 
The  book,  however,  quite  different  from  that  of  MM.  Zurcher 
and  Margolle,  is  valuable  as  presenting  the  extreme  views  of  the 
school  to  which  the  author  belongs,  and  as  extremely  ingenious 
in  its  defence  of  them,  although  thoroughly  wrong  in  its  fun- 
damental ideas,  —  as  much  so  as  one  would  be  who  should  en- 
deavor to  work  out  the  comparative  anatomy  of  the  elephant  by 
a  microscopic  examination  of  the  pimples  on  his  .hide. 

Mr.  Mallet's  book  is  as  different  from  either  of  the  others 
as  possible.  In  order  to  make  its  character  intelligible,  it 
will  be  necessary  to  give  some  idea  of  his  previous  publica- 
tions, and  of  those  of  other  really  scientific  investigators  in 
the  same  line  of  research,  and  to  show  how  and  when  this 
branch  of  geological  science  acquired  a  right  to  the  special 
name  it  now  bears,  that  of  SEISMOLOGY,  a  term  derived  di- 
rectly from  the  Greek,  and  signifying  the  Science  of  Earth- 
quakes. 

The  phenomena  of  volcanic  and  earthquake  action,  insepara- 
bly connected  in  tfye  popular  mind,  and  not  easily  disentangled 
from  each  other  by  the  scientific,  must  necessarily  engross  a 
large  share  of  thought  in  regions  where  they  are  frequently 
manifested,  and  especially  at  the  time  when  such  manifestations 
are  peculiarly  violent  or  destructive.  As  no  exhibition  of  the 
forces  of  Nature  is  so  sublime  as  that  of  the  volcano,  or  so  fear- 
ful in  its  consequences  as  that  of  the  earthquake,  it  was  natural 
not  only  that  allusions  to  these  phenomena  should  be  found  in  the 
oldest  writings  of  all  nations  inhabiting  regions  liable  to  such 
visitations,  but  that  their  very  cosmogonies  should  be  profoundly 


Earthquakes.  5 

affected  by  these  workings  of  unseen  forces.  Hence,  in  all  the 
sacred  writings  of  the  nations  inhabiting  the  vicinity  of  that  cra- 
dle of  civilization,  the  Mediterranean,  a  region  liable  to  earth- 
quakes, and  well  provided  with  volcanoes,  we  find  a  substratum 
of  belief  in  occasional  conflagrations  and  deluges  by  which  the 
gods  were  wont  to  arrest  the  career  of  human  wickedness,  and 
to  sweep  off  from  the  face  of  the  earth  its  inhabitants,  in  order 
to  make  way  for  a  new  and  improved  creation.  Such  ideas 
pervaded  the  Egyptian,  the  Hindoo,  the  Hebrew,  the  Arabian, 
and  the  Greek  mythology  ;  and  vestiges  of  the  same  are 
found  in  the  earthquake-shaken  regions  of  South  America ; 
while  we  are  not  aware  that  any  trace  of  them  can  be  discov- 
ered in  the  cosmogony  of  the  North  American  Indians,  dwell- 
ing in  a  region  but  little  liable  even  to  slight  earthquake 
shocks,  and  entirely  free  from  volcanoes.  • 

In  consequence  of  the  effect  which  violent  earthquake  shocks 
produce  on  the  material  progress  of  the  countries  subject  to 
them,  and  of  their  direct  relations  to  the  welfare  of  the  human 
race,  it  is  evident  that  these  and  kindred  events  stand  in  a 
different  relation  to  history  from  the  ordinary  phenomena  of 
geology.  Those  operations  of  Nature  which  proceed  slowly 
and  quietly,  without  destruction  of  life  and  property,  are  not 
so  calculated  to  excite  immediate  and  universal  attention  as 
those  which  are  accompanied  by  devastating  effects  over  vast 
regions.  Yet  the  former  class  may  in  reality  be  of  as  much 
importance  in  modifying  the  surface  of  the  globe,  and  may 
finally  bring  about  results  as  momentous,  as  any  immediate- 
ly following  great  earthquake  shocks  or  volcanic  eruptions. 
Thus,  slow  upheavals  or  depressions  of  large  areas  of  land  do 
really  produce  changes  profoundly  affecting  the  welfare  of 
great  numbers  of  people ;  but  these  changes  take  place  so 
slowly  that  they  are  prepared  for  beforehand,  and  their  effect 
is  spread  over  very  long  periods,  and  is  not  strikingly  per- 
ceptible at  any  one  moment.  That  such  changes  were  oc- 
curring in  past  times  is  clearly  demonstrated,  and  there  is 
every  reason  to  suppose  that  they  are  going  on  now.  Indeed, 
it  is  not  difficult  for  the  geologist  to  point  to  the  very  regions 
where  slowly,  but  surely,  the  ground  is  sinking  over  large 
areas,  and  where  alterations  in  the  distribution  of  sea  and 


6  Earthquakes. 

land  will  in  time  have  accumulated  sufficiently  to  produce 
materially  important  results  in  relation. to  vegetation,  animal 
life,  and  the  development  of  the  human  .race. 

In  view  of  the  above,  it  may  well  be  supposed  that  the 
number  of  volumes  devoted  to  descriptions  of  the  phenomena 
of  earthquakes  and  volcanoes,  in  all  languages,  is  very  great. 
M.  Alexis  Perrey  has  given  a  list  of  eighteen  hundred  and 
thirty-seven  works  on  earthquakes  published  up  to  1856  ;- 
but  he  admits  that  it  is  not  complete.  Those  relating  to 
volcanoes  and  volcanic  phenomena  are  undoubtedly  more  nu- 
merous, but  no  one  appears  to  have  set  about  making  a  full 
catalogue  of  them.  On  the  subject  of  Vesuvius  alone,  the  list 
of  volumes  and  scientific  papers  —  many  of  the  latter  much 
more  important  than  some  of  the  separate  works — would  em- 
brace many»hundred  titles,  perhaps  thousands.  Most  of  these 
works  are  purely  descriptive  of  the  incidents  observed,  as  the 
number  'of  persons  killed,  or  of  buildings  thrown  down ;  they  do 
not  attempt  to  philosophize  or  generalize,  or,  if  they  do,  it  is  in 
a  moral  or  religious  strain  rather  than  a  scientific  one.  The  de- 
scriptions of  volcanic  phenomena  are,  on  the  whole,  much  more 
satisfactory  than  those  of  earthquakes,  as  will  be  easily  under- 
stood. The  former  are  more  at  the  command  of  the  observer, 
are  longer  in  duration,  and  less  appalling  in  their  results. 
Earthquakes,  on  the  other  hand,  at  least  those  of  magnitude, 
come  unexpectedly,  give  no  indication  of  their  probable  violence 
or  duration,  and  so  unfit  the  mind  for  calm  observation  that 
it  is  only  by  previously  arranged  automatic  machinery  that  we 
can  expect  to  get  accurate  information  as  to  those  points  in  re- 
gard to  which  the  palpable  mementos  of  their  occurrence  are 
not  left  after  the  shock  has  subsided.  Hence  it  is  only  of  late 
years  that  earthquake  phenomena  have  begun  to  be  thoroughly 
investigated,  and  that  the  science  of  Seismology  has  taken  a 
position  among  those  branches  of  research  in  which  accuracy 
of  statement  is  expected. 

Since  history  has  preserved  more  or  less  complete  records 
of  earthquake  shocks,  in  various  parts  of  the  world,  from 
very  early  times,  it  would  naturally  be  inferred  that  light 
might  be  thrown  on  some  of  the  obscure  points  in  seismo- 
logical  science  by  carefully  collecting  and  tabulating  all 


Earthquakes.  7 

that  is  scattered  through  innumerable  published  volumes, 
in  regard  to  the  time,  place,  and  extent  of  earthquake  phe- 
nomena, and  that  this  would  be  the  necessary  preparation  for 
any  thorough  working-up  of  the  subject.  That  such  a  working- 
up  was  desirable  was  evident ;  for,  although  most  geologists, 
following  Humboldt  and  Buch,  were  pretty  clearly  in  accord 
with  regard  to  the  general  cause  of  volcanic  eruptions  and 
earthquakes,  yet  much  remained  to  be  done  to  make  the  modus 
operandi  of  the  internal  forces  more  clear,  and  especially  to 
furnish  material  for  combating  the  views  of  a  small  class  of 
geologists  who  persistently  refuse  to  adopt  the  views  formu- 
lated by  Humboldt,  and  desire,  on  the  other  hand,  to  refer  all 
these  phenomena,  as  far  as  possible,  to  local  causes,  as  will  be 
explained  farther  on. 

The  paper  read  by  Humboldt,  in  1823,  before  the  Berlin 
Academy,  "  On  the  Structure  and  Mode  of  Action  of  Volca- 
noes in  Different  Parts  of  the  Globe,"  contained  the  first  tru- 
ly philosophical  discussion  of  this  subject ;  and  the  ideas  with 
regard  to  the  origin  of  volcanoes  and  earthquakes,  then  first 
rather  vaguely  announced,  and  afterwards  more  clearly  formu- 
lated in  the  "  Cosmos  "  (J845), have  been  the  guiding  thread  by 
which  most  investigators  in  this  branch  of  science  have  endeav- 
ored to  work  their  way  through  the  labyrinth  of  difficulties  in 
which  they  have  found  themselves  involved.  The  grand  gen- 
eralization of  Humboldt,  by  which  the  whole  subject  of  the 
theory  of  these  phenomena  was  summed  up  in  a  few  words 
in  the  "  Cosmos,"  is  as  follows  :  "  In  a  comprehensive  view  of 
Nature's  operations,  all  these  [namely,  the  phenomena  of  vol- 
canism  and  earthquake  action]  may  be  fused  into  the  one  sim- 
ple idea  of  the  reaction  of  the  interior  of  the  earth  upon  its 
exterior"  Here  was  simply  and  concisely  enunciated  the 
guiding  principle  of  modern  structural  geology,  and  one  which, 
by  its  subsequent  connection  with  the  nebular  hypothesis,  has 
become  more  and  more  generally  recognized  as  the  corner- 
stone on  which 'the  science  rests.  It  is  certainly  true,  that, 
if  this  theory  be  not  adopted,  there  is  no  central  idea  in  the 
science,  nothing  about  which  it  can  crystallize,  and  that*  the 
whole  assemblage  of  facts  so  laboriously  collected  in  physical 
geology  is  without  anything  to  compact  it  into  one  harmo- 
nious whole. 


8  Earthquakes. 

Among  those  writers  who  have  devoted  considerable  time  to 
the  investigation  of  earthquake  phenomena,  besides  Humboldt, 
are :  Yon  Hoff,  in  whose  History  of  the  Changes  which  have 
taken  Place  in  the  Condition  of  the  Earth's  Surface  (Gotha, 
1822  -  41)  much  information  is  to  be  found ;  Friedrich  Hoff- 
mann, in  a  variety  of  elaborate  papers,  and  especially  in  his 
posthumous  works,  chiefly  published  between  1831  and  1839  ; 
F.  C.  Kries,  whose  work  on  the  Causes  of  Earthquakes  was 
crowned  and  published  by  the  Dutch  Academy  in  1820. 
Peter  Merian  also  made  an  elaborate  investigation  of  the 
earthquakes  occurring  at  Basle ;  Arago  published  several  valu- 
able papers  on  volcanoes  and  earthquakes,  from  1820  to  1824  ; 
and  Gay-Lussac  contributed  an  important  paper,  in  1823,  on 
the  theory  of  volcanoes,  in  which  was  the  first  definite  rec- 
ognition of  the  vibratory  character  of  earthquake  motions. 
In  1846,  Mr.  Robert  Mallet,  of  Dublin,  published  his  first  pa- 
per on  the  Dynamics  of  Earthquakes,  in  the  Transactions  of  the 
Royal  Irish  Academy.  In  1847?  Mr.  W.  Hopkins  furnished 
his  Report  on  the  Theories  of  Elevation  and  Earthquakes  to 
the  British  Association,  a  paper  which  has  been  much  quoted 
and  used  by  various  writers  on  geological  subjects.  M.  Alexis 
Perrey  is,  however,  undoubtedly  the  most  voluminous  writer  on 
earthquakes  ;  his  papers  and  publications  are  scattered  through 
a  great  number  of  the  Journals  and  Transactions  of  learned 
societies,  —  chiefly  those  of  the  French  and  Belgian  Acade- 
mies, —  and  bear  date  from  1841  to  1868  ;  the  latest  of  which 
we  have  learned  being  a  statistical  account  of  the  earthquakes 
of  Alaska.  In  the  British  Association  Report  for  1858  will 
be  found  a  list  of  M.  Perrey's  publications,  from  the  earliest 
down  to  1858,  including  fifty-nine  titles.  His  library  was  re- 
cently offered  for  sale,  and  was  shown  by  the  catalogue  to 
contain  four  thousand  and  fifteen  works  on  the  two  subjects  of 
earthquakes  and  volcanoes. 

Elaborate  and  valuable  as  M.  Perrey's  papers  are,  especially 
to  those  working  in  this  department  of  science,  they  are  chiefly 
statistical  in  their  nature,  and  cannot  be  compared  for  scope 
and  general  ability  with  those  of  Mr.  Mallet,  the  labors  of  the 
last-named  seismologist  being  not  only  those  of  a  compiler,  but 
also  of  an  original  experimenter  and  observer  in  this  field. 


Earthquakes.  9 

Mr.  Mallet's  results  have  been  laid  before  the  public  chiefly 
in  the  form  of  Reports  to  the  British  Association,  appearing  in 
the  volumes  for  1850, 1851, 1852,.  1853, 1854,  and  1858.  His 
principal  separate  publication  is  the  one  cited  at  the  .head  of 
this  article. 

In  the  Reports  of  the  British  Association  Mr.  Mallet  gives 
a  catalogue  of  all  recorded  earthquakes  from  1606  B.  c.  to 
1842  ;  but  for  the  discussion  of  the  subject  in  his  last  Report 
(1858)  he  uses  the  tabular  statements  of  M.  Perrey,  thus  sup- 
plementing his  own  work  by  that  of  M.  Perrey,  for  the  years 
1843-50.  All  the  catalogues  up  to  that  time  gave,  as  a  ba- 
sis for  induction,  more  or  less  precise  information  in  regard 
to  between  six  and  seven  thousand  earthquakes.  It  is  easy 
to  see,  that,  the  farther  we  go  back  in  time,  the  more  im- 
perfect the  records  of  earthquakes,  as  well  as  of  all  other 
physical  events,  will  be  found  to  be.  As  Mr.  Mallet  remarks, 
in  speaking  of  the  curves  he  has  drawn,  illustrating  the  fre- 
quency of  recorded  earthquakes  during  the  different  centuries :  . 
"  Our  chrono-seismic  curve  is,  in  fact,  not  only  a  record  of 
earthquakes,  but  a  record  of  the  advance  of  human  enterprise, 
travel,  .and  observation."  Thus,  for  the  years  1700  to  1400 
B.  c.  there  are  a  few  scattered  facts ;  then,  from  1400  to  900, 
nearly  five  hundred  years  of  perfect  blank  ;  followed  again, 
with  a  few  exceptions,  by  another  blank  from  800  to  600  B.  c. 
Indeed,  the  only  record  of  any  value  for  scientific  analysis 
commences  about  500  B.  c.  Since  that  time,  the  epochs  of 
the  invention  of  printing  and  of  the  Reformation  are  clearly 
marked  in  the  expansions  of  the  curves;  while  the  discovery 
of  America,  the  voyage  to  India  around  the  Cape  of  Good 
Hope,  and  the  vast  increase  in  the  commercial  intercourse  of 
the  world  consequent  thereon,  are  also  perfectly  recognizable 
in  the  rapid  accumulation  of  data,  and  the  sudden  swelling 
of  the  curve  of  frequency.  While  only  six  or  seven  thousand 
earthquakes  have  been  tabulated  for  all  time  down  to  1850,  a 
German  author,  Dr.  K.  E.  Kluge,  was  able  to  obtain  records  j 
of  four  thousand  six  hundred  and  twenty  as  occurring  between  ? 
the  years  1850  and  1857,  inclusive. 

We  will  now  endeavor  to  present,  with  a  few  additions  of 
our  own,  the  most  important  results  obtained  by  the  various 


10  Earthquakes. 

authors  specified,  in  working  over  the  great  mass  of  statistical 
information  which  has  been  accumulated. 

Earthquakes  maybe  considered, first, with  reference  to  their 
geographical  distribution,  or  the  position  which  seismic  areas 
occupy  on  the  earth's  surface  with  reference  to  each  other, 
to  the  great  features  of  the  earth's  surface,  and  to  the  position 
of  areas  where  kindred  phenomena  —  as,  for  instance,  volcanic 
eruptions  —  are  manifested  ;  second,  in  their  relations  of  time, 
or  with  reference  to  their  occurrence,  as  connected,  synchro- 
nously or  otherwise,  with  changes  of  the  seasons,  or  as  recur- 
ring in  cycles,  or  as  influenced  by  the  position  of  the  heavenly 
bodies,  especially  the  moon  or  the  sun  ;  and,  lastly,  as  con- 
nected with  movements  or  conditions  of  the  atmosphere,  or 
with  electrical  and  magnetic  disturbances. 

Let  us  examine,  first,  what  deductions  can  be  drawn  from 
the  geographical  position  of  earthquake  areas. 

There  are  several  "  seismographic  maps,"  showing  the  geo- 
graphical distribution  of  earthquake  regions  ;  among  these,  the 
best  and  latest  is  that  accompanying  Mallet's  Fourth  Report  to 
the  British  Association,  and  from  which  the  others  do  not  dif- 
fer much  in  the  general  character  of  the  results  shown.*  The 
first  impression  produced  by  looking  at  any  of  these  should  be 
rather  one  of  alarm ;  for  nearly  the  whole  of  the  inhabited  and 
habitable  earth  appears  to  be  shaded  with  the  various  tints 
implying  a  greater  or  less  liability  to  earthquake  shocks.  It 
would,  indeed,  seem,  at  first  sight,  as  if  only  those  regions  were 
left  uncolored  in  regard  to  which  no  information  could  be 
obtained.  Thus,  all  of  Europe  is  more  or  less  deeply  colored^ 
except  a  part  of  Central  and  Northeastern  Russia, —  and  nearly 
all  of  Asia,  except  the  extreme  northern  portion  of  Siberia,  and 
the  country  drained  by  the  Amoor  River.  On  the  other  hand, 
almost  the  whole  of  Africa  and  Australia  is  left  blank,  as  well 
as  the  extreme  northern  portion  of  North  America,  and  all  of 
South  America  east  of  the  eastern  base  of  the  Andes  and 
south  of  a  narrow  belt  extending  around  from  New  Granada 
to  French  Guiana.  It  is  evident  that  portions  of  the  areas 
thus  omitted  in  the  distribution  of  the  earthquake  tint  must 
have  been  left  blank  on  account  of  the  absence  of  information 
in  regard  to  their  seismic  character.  Indeed,  it  might  be 


Earthquakes.  .       11 

asked  whether  there  is  any  part  of  the  world  where  earth- 
quakes do  not  occur.  To  this  question  it  would  probably  be 
safe  to  reply,  that  there  is  no  region  thickly  inhabited  by  a  civ- 
ilized people,  and  where  consequently  there  is  a  pretty  complete 
record  of  what  has  happened  for  a  considerable  period  back,  in 
which  there  are  not  occasional  slight  manifestations  of  seis- 
mic energy.  But  it  is  pretty  certain,  on  the  other  hand,  that 
regions  so  well  known  as  Brazil,  or  as  some  portions  of  the  coast 
of  Africa,  could  not  be  much  troubled  by  earthquakes  without 
some  information  having  been  gathered  in  regard  to  them  by 
the  many  travellers  who  have  visited  those  countries.  The 
fact  that  any  area  is  left  uncolored  in  Mr.  Mallet's  map  is  a 
strong  reason  for  believing  that  it  is  probably  not  liable  to 
severe  shocks.  Leaving  Africa  and  Australia  out  of  the  ques- 
tion, as  too  little  known  to  allow  of  positive  statements  being 
made  concerning  them,  it  may  be  said  that  there  is  hardly 
any  portion  of  the  habitable  globe  which  is  not  occasionally 
shaken,  but  that  Eastern  South  America  comes  nearest  to  a 
desirable  state  of  security  in  this  respect.  Most  of  British 
North  America  is  also  very  firm  in  its  position  as  an  integral 
part  of  the  crust,  but  is  not  likely  ever  to  be  very  thickly 
inhabited. 

On  close  examination  of  Mr.  Mallet's  map,  we  see  upon  it 
three  tints  of  color,  intended  to  distinguish,  as  we  learn  from  the 
accompanying  report,  the  relative  intensity  of  the  shocks  occur- 
ring in  the  regions  designated  by  them.  The  deepest  tint  indi- 
cates great  earthquakes  ;  the  middle  tint,  those  of  mean  inten- 
sity ;  the  lightest  color,  minor  shocks*  By  "  great  earthquakes  " 
are  meant  those  in  which,  over  large  areas,  numerous  cities  or 
towns  are  overthrown,  persons  killed,  rocky  masses  dislocated, 
etc. ;  under  the  head  of  earthquakes  of  mean  intensity  are 
included  such  as  were  felt  over  a  wide  area,  but  which  were 
not  severe  enough  to  have  a  very  destructive  effect,  and  were 
not  attended  with  much  loss  of  life.  The  third  class  em- 
braces those  slight  tremors  of  the  surface  which  do  not  pro- 
duce any  serious  destruction  or  commotion,  and  which  leave 
but  few,  if  any,  traces  of  their  occurrence. 

It  will  of  course  be  impossible,  in  these  pages,  to  enter  into 
any  minute  discussion  of  the  distribution  of  the  different  bands 


12  Earthquakes. 

of  seismic  energy ;  but  some  general  idea  of  their  geographical 
range  can  be  given.  Let  us  examine,  first,  the  position  of  the 
patches  of  deepest  tint,  —  those  indicating  the  occurrence  of 
"  great  earthquakes."  We  see  at  once  that  the  area  thus 
colored  is,  to  a  very  large  extent,  coincident  with  that  of  the 
greatest  displays  of  active  volcanic  forces.  As  the  whole  Pa- 
cific coast  of  America  and  the  islands  of  the  coast  of  Asia  are 
the  scene  of  volcanic  phenomena  on  the  grandest  scale,  so,  too, 
the  darkest  tint  of  color  follows  the  coast  of  the  Pacific  Ocean 
around,  indi«ating  great  earthquakes  along  nearly  the  whole 
line ;  and  when  this  is  not  the  case,  then  the  color  represent- 
ing the  prevalence  of  shocks  of  the  second  order  of  intensity 
is  given.  The  great  circle  of  fire  about  Borneo  as  a  centre, 
extending  from  Manila  around  to  Sumatra,  exhibits  a  broad 
belt  of  the  deepest  tint.  The  same  is  true  of  the  region  con- 
necting the  Andes  with  the  Lesser  Antilles.  Iceland,  the  Azores, 
the  Canaries,  the  Cape  Verdes,  parts  of  Italy,  the  country  be- 
tween the  Mediterranean  and  the  Caspian,  —  these  are  all  re- 
gions of  great  earthquakes,  and  also,  as  we  well  know,  of  great 
volcanic  eruptions.  Of  regions  liable  to  great  earthquakes  and 
not  volcanic,  the  following  may  be  cited  as  the  principal :  por- 
tions of  the  coast  of  China,  the  region  about  the  mouth  of  the 
Ganges,  and  that  south  of  the  mouth  of  the  Indus,  the  Pyre- 
nees, and  the  coast  of  Portugal  between  Lisbon  and  Oporto. 
If  we  should  (as  we  very  properly  might)  distinguish  in  the 
region  of  great  earthquakes  two  divisions,  —  one  in  which 
highly  destructive  shocks  may  be  expected  to  occur  frequently, 
and  the  other  where  they  take  place  only  at  long  intervals, 
—  we  should  then  find  that  the  former,  that  is  to  say,  the 
pre-eminent  earthquake  areas  of  the  world,  are  strictly  limited 
to  regions  of  volcanic  activity,  or  to  parts  of  the  earth  where 
such  activity  has  only  died  out  in  the  most  recent  geological 
periods.  To  say  also  that  these  regions  of  great  earthquake 
shocks  are  almost  exclusively  in  the  neighborhood  of  the 
ocean  is,  then,  almost  unnecessary ;  since  we  know  very  well 
that  there  are  almost  no  active  volcanoes  in  existence  except 
near  the  sea,  —  those  reported  in  the  Chinese  annals  as  occur- 
ring in  the  Thian-Shan  range,  north  of  the  Gobi  Desert,  being 
the  only  exceptions,  while  with  regard  to  these  there  is  much 


Earthquakes.  13 

uncertainty.  The  two  most  prominent  facts,  then,  in  respect 
to  regions  liable  to  great  earthquakes  are,  that  they  are  almost 
entirely  coincident  with  areas  of  active  volcanoes,  and  that 
they  also  lie  near  the  borders  of  the  ocean. 

Taking  next  into  consideration  the  areas  of  earthquake  shocks 
of  moderate  intensity,  we  find  that  they  also  (since  the  greater 
includes  the  less)  are  near  coast-lines  and  volcanic  centres, 
either  those  now  active  or  else  such  as  have  become  recently 
extinct,  and  especially  that  broad  bands  of  the  tint  peculiar  to 
this  class  are  found  along  many  of  the  great  ranges  of  moun- 
tains which  are  not  volcanic,  notably  at  the  base  of  the  Hima- 
layas, the  Alps,  and  the  Pyrenees, —  also  on  the  northern  edge 
of  the  plateau  of  High  Asia,  through  the  belt  of  islands  off  the 
east  coast  of  Australia,  from  New  Guinea  around  to  New  Zea- 
land, and  in  the  extinct  volcanic  islands  of  the  Atlantic  Ocean, 
—  as  Ascension,  St.  Helena,  Tristan  d'Acunha,  etc. 

Here,  before  going  any  farther,  it  will  be  well  to  speak  of  the 
very  inaccurate  ideas  apt  to  be  given  by  earthquake  catalogues 
of  the  real  number  and  severity .  of  shocks,  and  from  a  very 
natural  cause.  In  the  regions  where  earthquakes  are  of  rare 
occurrence,  and  never  severe,  the  slightest  vibration  is  a  mat- 
ter of  great  interest,  much  talked  about,  and  of  course  greatly 
exaggerated ;  especially  are  the  newspaper  accounts  likely  to- 
represent  such  uncommon  events  in  the  liveliest  colors.  In  a 
really  earthquake-shaken  region,  like  the  west  coast  of  South 
America,  and  where  at  the  same  time  newspapers  are  almost 
unknown,  by  far  the  greater  number  of  shocks  are  never  put 
on  record,  or  at  least  they  have  not  been  until  since  the  es- 
tablishment of  public  scientific  observatories,  and  of  these 
there  are  but  very  few,  —  while  in  thickly  settled  and  highly 
civilized  regions  each  slightest  jar  of  the  ground  has  been 
recorded.  This  leads  to  curious  results  in  the  records,  and 
might  cause  very  erroneous  conclusions  to  be  drawn  in  regard 
to  the  real  earthquake  character  of  different  regions.  Thus 
it  appears,  by  the  catalogues,  that  nearly  as  many  earthquakes 
have  taken  place  in  Great  Britain  during  the  nineteenth  cen- 
tury as  in  Chile,  —  while  we  know  that  in  the  first-named  coun- 
try no  very  destructive  shock  has  ever  taken  place,  and  that 
even  minor  ones  are  very  rare.  In  Chile,  on  the  contrary, 


14  Earthquakes. 

several  very  frightful  earthquakes  have  occurred  during  the 
present  century ;  one  hundred  and  twenty-seven  shocks  were 
felt  at  Santiago  in  thirty-five  months,  and  prudent  people 
decline  ever  to  sleep  in  a  room  with  the  door  shut,  lest  it 
may  become  jammed  by  an  earthquake,  and  egress  be  ren- 
dered impossible.  It  is  a  sufficient  proof  that  a  region  is 
comparatively  safe  from  real  danger,  to  read  as  follows : 
"Newport,  R.  I.,  1766,  August  25.  Violent  shock.  No 
damage  done"  A  violent  shock  not  producing  any  damage 
would  be  a  desideratum  on  the  South  American  coast,  where 
probably  the  record  would  have  stood  :  "  A  very  slight  vibra- 
tion. No  damage  done." 

It  is  from  considerations  like  those  just  suggested,  and 
also,  in  some  degree,  through  the  absence  of  reliable  data, 
and  the  habit  which  our  newspapers  have  of  exaggerating 
all  events,  whether  physical  or  political,  that  we  may  ac- 
count for  the  seismological  character  of  our  own  country  be- 
ing very  much  misrepresented  on  Mr.  Mallet's  map.  On  it 
we  find  the  whole  region  east  of  the  meridian  of  95°,  except- 
ing a  small  area  about  the  Upper  Great  Lakes,  colored  of  the 
middle  tint,  indicating  a  region  of  considerable  earthquake 
activity.  This  band  is  also  extended  up  to  the  head  of  the 
Missouri  River,  over  a  belt  of  country  two  hundred  miles  wide. 
On  the  Pacific  coast,  on  the  other  hand,  a  broad  band  of  the 
lightest  tint,  indicating  only  an  occasional  visitation  of  the 
lightest  possible  shocks,  extends  back  from  the  ocean  as  far  as 
Salt  Lake,  including  the  region  north  and  south  between  the 
mouth  of  the  Colorado  and  the  northern  line  of  California. 
This  tint  is  also  continued  up  the  coast  to  the  Aleutian  Isl- 
ands, excepting  only  a  small  area  about  the  mouth  of  the 
Columbia  River,  where  two  active  volcanoes  are  inserted,  and, 
apparently  in  consequence  of  their  presence,  the  region  there- 
about is  colored  of  the  middle  tint. 

Now  certainly  our  personal  experience  —  and  this  is  well 
supported  by  the  catalogues  —  shows  that  we  live  in  a  region 
where  earthquakes  are  very  little  to  be  apprehended,  and 
where  there  is  no  record  of  any  destructive  one  ever  having 
taken  place.  We  have  no  remembrance  of  ever  experien- 
cing a  shock,  even  of  the  slightest  kind,  in  Massachusetts. 


Earthquakes.  15 

We  have  to  go  back  as  far  as  1755  to  find  any  record  of  a  de- 
cided earthquake,  and  this  seems  to  have  been  connected  with 
a  great  agitation  extending  over  a  large  part  of  the  earth's 
surface,  and  it  is  not  unlikely  that  the  focus  of  disturbance 
was  far  out  at  sea.  It  will  be  remembered  that  the  "  Great 
Lisbon  Earthquake  "  commenced  November  1,  1755,  and  that 
it  was  one  of  the  most  violent  and  widely  extended  on  record. 
The  shocks  continued,  at  various  places  around  the  Mediter- 
ranean, with  occasional  intervals,  for  many  months,- and  nearly 
the  whole  circumference  of  the  Atlantic  Ocean  was  in  a  dis- 
turbed condition,  while  portions  of  the  East  India  Islands  were 
also  vibrating  synchronously,  if  not  sympathetically,  with  the 
other  side  of  the  globe. 

The  shock  of  November  18,  1755,  was  felt  all  along  the 
Atlantic  coast,  between  Halifax  and  Maryland,  and  west  cer- 
tainly as  far  as  Lake  George,  in  New  York.  It  was  quite 
severe  at  Boston,  —  more  so,  probably,  than  anywhere  else 
within  our  territory.  This  earthquake  was  described  by  Pro- 
fessor Winthrop,  of  Harvard  College,  in  the  Philosophical 
Transactions  of  the  Royal  Society  (Vol.  L.  Part  i.  p.  l)y 
with  considerable  detail,  and  with  no  little  skill  and  critical 
acumen.  The  shock  was  violent  enough  to  throw  down  a  con- 
siderable number  of  chimneys  and  the  gable  ends  of  some 
brick  buildings.  Throughout  the  State  many  stone  fences 
were  more  or  less  injured.  Some  cracks  were  made  in  the 
ground  near  Scituate,  from  which  water  and  sand  issued,  to- 
the  extent  of  "  many  cart-loads."  Previously  to  that,  in  1638, 
1658,  1662,  and  1727,  shocks  had  been  felt  in  Boston,  of 
which  that  of  1662  was  severe  enough  to  throw  down  some 
chimneys.  It  does  not  appear,  however,  that  any  person  has 
ever  been  killed  by  any  earthquake  in  New  England  ;  so  that 
it  is  pretty  safe  to  conclude  that  some,  if  not  all,  of  the 
chimneys  thrown  down  had  been  built  with  very  poor  mortar. 
We  are  not  aware  that  therfc  is  any  record  of  any  consid- 
erable shock  having  taken  place  in  New  England  since  that 
of  1755. 

On  the  Pacific  coast  of  the  United  States,  however,  hardly  a 
year  elapses  without  some  pretty  severe  shock.  The  number 
of  earthquakes  recorded  in  California  for  the  thirteen  years 


16  Earthquakes. 

ending  December,  1863,  is  one  hundred  and  eleven.  Many 
very  heavy  ones  have  occurred  there  since  the  beginning  of  the 
present  century.  In  1812  the  whole  southern  part  of  that  State 
was  violently  agitated  during  four  and  a  half  months.  In  some 
regions  the  inhabitants  abandoned  their  houses  altogether. 
Several  of  the  "Missions"  —  substantial  stone  buildings  — 
were  thrown  down ;  in  one  —  that  of  San  Luis  Capistrano  — 
religious  services  were  going  on  at  the  time,  and  many  of  those 
present  were  killed,  the  number  of  persons  thus  perishing  be- 
ing stated  by  various  authorities  at  from  thirty  to  forty-five. 
A  number  of  lives  were  also  lost  at  the  Missions  of  La  Purissi- 
ma,  one  hundred  and  twenty  miles  distant  from  that  of  San 
Luis  Capistrano.  It  must  be  recollected  that  the  State,  then 
the  Mexican  province  of  Upper  California,  was  at  that  time 
extremely  thinly  inhabited.  Had  it  been  a  populous  region, 
it  would  seem,  from  the  descriptions  of  the  character  of  the 
shocks,  that  the  loss  of  life  and  property  must  have  been  very 
great.  Among  the  earthquakes  which  have  happened  in  Cali- 
fornia since  it  became  a  part  of  our  own  territory,  two  are  par- 
ticularly to  be  remembered,  —  those  of  October  8, 1865,  and  of 
October  21, 1868.  The  first  did  considerable  damage  to  prop- 
erty in  San  Francisco,  and  the  other  was  severely  felt  over  an 
extensive  area,  demolishing  a  great  number  of  buildings  in  that 
city,  and  especially  in  the  towns  on  the  opposite  side  of  the 
bay  between  Oakland  and  San  Jose*.  Several  persons  were 
killed  by  falling  fragments.  In  view  of  the  above-cited  facts, 
it  will  readily  be  seen  that  even  coloring  both  sides  of  the 
United  States  as  equally  liable  to  seismic  demonstrations 
would  not  at  all  be  supported  by  the  facts ;  while  representing 
the  Atlantic  coast  as  more  shaky  than  the  Pacific  slope  is 
very  far  out  of  the  way. 

The  extending  of  a  band  of  color  indicating  serious  earth- 
quake action  up  the  Valley  of  the  Missouri  is  also  quite  un- 
supported by  the  facts.  It  is  true,  however,  that  a  region  of 
a  few  hundred  square  miles  in  area,  near  the  junction  of  the 
Mississippi  and  the  Missouri  Rivers,  was  subjected  to  violent 
earthquake  shocks  during  several  months,  in  the  years  1811  - 
12,  —  a  remarkably  exceptional  case  in  every  respect,  and 
therefore  worthy  of  a  brief  notice.  This  disturbance  com- 


Earthquakes.  17 

menced  December  16, 1811,  with  an  earthquake  which  was  felt 
over  a  large  portion  of  the  Valleys  of  the  Mississippi,  the  Ohio, 
and  the  Arkansas  ;  it  was  also  noticed  as  far  to  the  southeast 
as  Florida,  although  the  shocks  were  feeble  to  the  east  of  the 
Alleghanies.  New  Madrid,  on  the  Mississippi,  in  latitude  37° 
45',  a  little  below  the  mouth  of  the  Ohio,  seemed  to  be  the  fo- 
cus of  the  disturbance,  and  the  shocks  continued  there  daily 
and  almost  hourly  for  several  months ;  they  are  reported  .as 
having  finally  ceased  about  the  time  of  the  great  earthquake  of 
Caracas,  March  26,  1812.  As  a  result  of  this,  a  large  tract 
of  country  west  of  New  Madrid,  extending  seventy  or  eighty 
miles  north  and  south,  and  thirty  east  and  west,  was  perma- 
nently sunk  considerably  below  its  former  level,  and  converted 
into  a  marsh.  This  was  truly  an  interesting  and  peculiar  occur- 
rence, as  it  is  almost  the  only  instance  on  record  of  a  region 
far  from  volcanoes,  from  mountain  chains,  and  from  the  ocean, 
being  subjected  to  a  long  and  violent  disturbance  of  this  kind ; 
it  is  also  remarkable  that  the  heavy  shocks  in  this  locality 
have  been  repeated  only  once,  so  far  as  we  are  able  to  learn, — 
namely,  in  1865,  August  17,  when  a  considerable  part  of  the 
Mississippi  Valley  was  shaken  with  some  violence,  although  no 
serious  damage  was  done  at  any  point.  The  shock  was  most 
distinctly  felt  at  New  Madrid.  It  is  said  that  light  vibrations 
have  frequently  occurred  in  the  district  of  the  "  Sunk  Coun- 
try," as  it  is  called,  since  the  great  ones  of  1811-12. 

An  examination  of  the  catalogues  and  maps  of  earthquake 
areas,  with  a  view  to  their  correlation  with  the  geological  struc- 
ture of  those  areas,  shows  some  very  interesting  facts.  It  is 
clear  that  persons  living  on  the  older  geological  formations 
have  much  less  reason  to  apprehend  earthquake  disturbances 
than  those*  who  have  under  them  the  more  recent  members  of 
the  series.  There  is  hardly  any  region  liable  to  severe  shocks 
where  there  are  not,  in  the  vicinity  at  least,  large  accumula-  (  ^ 
lions  of  strata  belonging  to  one  of  the  later  geological  epochs. 
Chains  of  mountains  made  up  of  Palaeozoic  rocks,  as,  for  in- 
stance, the  Urals,  the  Appalachians,  the  Brazilian  ranges,  the 
Scandinavian  mountains,  and  the  Laurentian  mountains,  are 
never  the  scene  of  violent  or  destructive  shocks. 

Where  the  newer  formations  do  exist,  but  where,  however, 
2 


18  Earthquakes. 

they  remain  undisturbed,  or  nearly  in  the  same  relative  posi 
tion  in  which  they  were  deposited,  there,  too,  is  immunity  from 
earthquake  damage,  and,  a  fortiori ,  where  the  older  formations 
occur  and  are  entirely  undisturbed.  Thus,  the  whole  vast  re- 
gion of  the  Central  and  Northern-Central  portions  of  North 
America,  north  of  the  parallel  40°,  is  remarkably  free  from 
earthquakes,  and  we  have  there  one  of  the  largest  areas  in  the 
world  of  nearly  horizontally  stratified  Palaeozoic  rocks.  From 
the  western  base  of  the  Appalachian  chain,  towards  the  north- 
west, over  a  wide  belt,  including  the  Upper  Great  Lakes,  and 
trending  off  towards  the  Arctic  Ocean,  there  extends  a  tract 
embracing  many  hundred  thousand  square  miles,  and  included 
between  the  eastern  base  of  the  Cordilleras  and  Hudson's  Bay, 
over  which  only  the  oldest  geological  formations  occur,  and 
where  these  have  remained  almost  wholly  undisturbed  since 
their  original  deposition.  This  is  a  region  left  entirely  uncol- 
ored  in  the  seismological  maps,  and  which,  so  far  as  can  be 
learned,  is  indeed  almost,  if  not  quite,  exempt  from  even  the 
minor  earthquake  shocks.  So,  too,  the  region  of  the  Plains 
in  our  own  territory,  although  underlaid  by  the  more  recent 
formations,  is  little,  if  at  all,  troubled  by  earthquakes,  and  we 
know  that  the  formations  are  here  also  almost  horizontal.  The 
same  conditions  may  be  traced  all  over  the  world,  so  far  as  our 
information  goes  ;  so  that  we  'are  justified  in  asserting  that  it 
is  extremely  rare  to  find  earthquakes  occurring  over  geologi- 
cally undisturbed  areas,  or  regions  where  the  strata  have  not 
been  turned  up  and  folded,  and  that  the  same  is  true  even 
where  such  geological  disturbances  have  taken  place,  provided 
they  have  not  been  continued  down  to  a  recent  geological 
period. 

Thus  we  have  shown,  that,  from  a  geographical  point  of  view, 
great  earthquakes,  and  even  those  of  minor  consequence,  are 
clearly  connected  in  their  place  of  occurrence  with  the  position 
of  the  oceanic  basins,  with  the  existence  of  great  mountain* 
chains,  and  consequently  with  the  distribution  of  volcanoes  ; 
also,  that  they  are  unmistakably  associated  with  the  existence 
of  the  more  recent  geological  formations,  and  with  their  most 
disturbed  condition.  Hence  we  have  the  strongest  reasons  for 
believing  that  earthquake  phenomena  are  dependent  on  gen- 


Earthquakes.  19 

eral  laws,  such  laws  as  have  governed  the  building  up  of  con-" 
tinents  and  the  bringing  of  the  great  features  of  the  earth  into 
their  present  stage  of  development.  They  cannot  be  mere  lo- 
cal phenomena,  occurring  without  any  mutual  relations  to  each 
other,  or  as  disconnected  with  the  whole  series  of  geological 
events  which  scientific  investigations  show  so  clearly  to  have 
been  governed  by  a  law  of  progress.  The  same  conclusion 
may  be  drawn  from  a  consideration  of  the  extent  over  which 
many  earthquake  shocks  are  felt,  —  the  magnitude  of  the 
area  shaken,  and  its  proportion  to  the  whole  surface  of  the 
earth,  being  considered,  very  fairly  as  it  would  seem,  a  de- 
cided indication  of  the  magnitude  of  the  cause.  One  of  the 
greatest  earthquake  shocks  on  record  is  that  already  referred 
to  as  uthe  Great  Lisbon  Earthquake,"  the  centre  of  disturbance 
having  been  situated  near  the  coast  of  Portugal,  and  the  effects 
of  the  shock  having  been  most  fearful  at  that  city.  This  earth- 
quake produced  sensible  effects  over  an  area  of  the  earth's  sur- 
face included  between  Morocco  on  the  south  and  Iceland  on  the 
north,  Toplitz  in  Bohemia  on  the  east,  and  the  West  India  Isl- 
ands on  the  west.  The  great  earthquake  of  August  13, 1868, 
of  which,  however,  only  the  most  unsatisfactory  accounts  have 
yet  reached  us,  appears  to  have  been  felt  along  the  Andes,  over 
a  breadth  of  forty  degrees  of  latitude,  and  its  effects  were  dis- 
tinctly visible  in  the  great  waves  if  raised  at  Juan  Fernandez, 
on  all  the  Hawaiian  Islands,  on  the  coast  of  Japan,  and  even  in 
Australia  and  New  Zealand. 

On  examining  the  phenomena  of  earthquakes  with  refer- 
ence to  the  time  of  their  occurrence,  various  interesting  results 
have  been  obtained,  as  respects  their  frequency,  both  at  dif- 
ferent seasons  of  the  year,  and  while  the  earth  is  in  certain 
positions  with  regard  to  the  sun  and  moon.  It  appears,  also, 
that  there  are  certain  periods  during  which  the  earth  is  in  a 
peculiarly  disturbed  condition,  and  that  not  unfrequently  a  large 
number  of  shocks  take  place  at  about  the  same  time  in  regions 
far  removed  from  each  other.  As  a  marked  instance  of  this, 
may  be  mentioned  the  latter  part  of  November,  1852,  when  a 
large  portion  of  the  Pacific  coast,  both  of  North  and  South 
America,  was  in  motion,  at  the  same  time  with  the  whole  of 
the  East  Indian  Archipelago  and  various  intermediate  places. 


20  Earthquakes. 

• 

This  earthquake  period  commenced  in  the  East  Indies,  in  South- 
ern Sumatra,  on  the  llth  of  November,  and  the  shocks  con- 
tinued in  various  parts  of  the  Archipelago  until  the  26th,  when 
the  great  one  took  place  which  was  felt  all  over  the  East  India 
Islands,  from  Manila  to  Sumatra.  The  disturbance  was  kept  up 
through  the  whole  of  December,  and,  on  the  21st  of  that  month, 
had,  in  the  island  of  Java,  reached  a  degree  of  violence  exceed- 
ing anything  previously  known.  From  the  27th  to  the  30th 
of  November  the  earth  was  in  constant  motion  in  all  the  East 
India  Islands.  During  exactly  these  days,  — that  is,  from  the 
26th  to  the  29th  of  November,  —  tremendous  shocks  were  con- 
stantly felt  in  the  Great  Antilles.  On  the  26th  of  November, 
very  severe  earthquakes  agitated  the  Pacific  coast  of  North 
America,  from  Mexico  to  Northern  California,  and  indeed  the 
whole  region  between  the  Colorado  River  and  the  coast  was  in 
a  state  of  continual  vibration  for  nearly  two  months.  On  the 
same  day,  November  26th,  an  earthquake  was  felt  in  Italy; 
the  next  day,  a  slight  shock  on  the  Atlantic  coast  of  the  United 
States,  and  a  heavy  one  on  the  South  American  coast ;  and  still 
the  next,  another  in  Chile.  It  would  appear  that  at  this  time 
both  sides  of  the  Pacific  Ocean,  from  China  to  Australia  on  the 
west,  and  between  California  and  Chile  on  the  east,  were  vibrat- 
ing synchronously  and  extensively,  and  that  this  condition  of 
things  lasted  for  nearly  two  months,  while  several  points  in 
other  regions  were  also  seriously  implicated  in  the  disturb- 
ance. This  was  undoubtedly  one  of  the  grandest  epochs  of 
earthquake  disturbance  which  have  ever  been  known,  and  it  is 
hardly  possible  to  explain  the  synchronous  occurrence  of  so 
long-continued  and  violent  a  series  of  shocks  in  the  regions 
affected  by  simply  considering  it  as  an  accidental  coincidence. 
A  great  many  other  instances  might  be  cited  of  earthquake 
disturbances  taking  place  at  the  same  time,  in  regions  far  dis- 
tant from  each  other ;  while,  on  the  other  hand,  it  is  true  that 
severe  shocks  have  often  taken  place  which  were  limited  to 
quite  a  narrow  area. 

The  coincidences  of  earthquakes  and  volcanic  activity  are 
curious,  and  not  easily  brought  into  harmony  with  any  theory. 
The  great  fact  is  clear  enough,  that  by  far  the  most  severe  and 
the  most  frequent  earthquake  shocks  are  in  countries  of  vol- 


Earthquakes.  21 

canic  activity.  But  it  is  also  not  to  be  denied  that  volcanic 
eruptions  do  occur  occasionally  in  perfect  quiet,  so  far  as  vibra- 
tions of  the  adjacent  crust  are  concerned.  The  same  uncer- 
tainty exists  with  regard  to  the  internal  connections  and 
sympathy  of  volcanic  vents,  whether  at  a  distance  from  or  near 
to  each  other.  Cases  have  repeatedly  occurred  where  adjacent 
volcanoes  have  not  sympathized  in  the  slightest  degree  in  their 
periods  of  rest  and  activity,  even  tflien  in  immediate  proxim- 
ity to  each  other.  One  of  the  most  curious  of  these  instances 
is  that  of  the  summit  crater  of  Mauna  Loa,  and  Kilauea,  the 
famous  side-crater  on  the  same  mountain,  nearly  ten  thousand 
feet  lower  down.  It  has  repeatedly  happened  that  the  upper 
one  has  been  in  violent  eruption,  while  the  lower  was  in  no  de- 
gree more  active  than  usual,  thus  showing  that  the  two  great 
vents  of  the  same  volcano  were  not  in  immediate  connection. 
On  the  other  hand,  it  has  often  occurred,  that,  of  two  volcanoes 
near  each  other,  or  even  at  a  considerable  distance  apart,  one 
has  become  absolutely  quiet  at  the  very  moment  when  the 
other  has  suddenly  burst  into  eruption ;  the  instances  of  this 
kind  are,  some  of  them,  so  marked,  and  the  correspondences 
in  the  commencement  or  termination  of  the  seasons  of  activity 
have  been  so  exact,  that  it  would  be  quite  impossible  to  pass 
them  over  as  mere  accidental  coincidences. 

The  question  has  been  much  discussed,  whether  volcanoes 
in  reference  to  earthquakes  act  as  "  safety-valves,' '  —  that  is, 
whether  their  eruptions,  once  commenced,  can  be  looked  upon 
as  in  any  degree  removing  the  probability  of  violent  shocks. 
That  such  is  the  case  is  the  almost  universal  belief  through 
earthquake-shaken  regions  in  the  neighborhood  of  great  volca- 
noes. Indeed,  it  seems  not  unreasonable  to  suppose,  that,  the 
internal  forces  having  once  found  vent  for  their  energy  in  the 
eruptive  action,  the  vibration  of  the  crust,  which  can  hardly 
be  looked  on  as  anything  else  than  the  result  of  the  struggles 
between  expansive  force  on  the  one  hand  and  the  pressure 
and  tenacity  of  the  superincumbent  material  on  the  other,  would 
be  suspended.  On  examining  the  records,  it  will  be  found  that 
there  are  many  instances  which  show 'clearly  that  earthquake 
shocks,  previously  severe,  have  ceased  entirely  at  the  moment 
of  the  eruption  of  some  adjacent  volcano  ;  while  there  are  other 


22  Earthquakes. 

instances  in  which  severe  earthquakes  have  been  felt  some 
time  after  great  eruptions  in  the  vicinity  had  commenced.  In 
the  very  numerous  instances  where  volcanic  eruptions  have 
been  the  signal  for  the  stoppage  of  a  long  series  of  earthquake 
shocks  in  the  vicinity,  it  is  difficult  to  admit  any  other  explana- 
tion than  that  the  issuing  of  the  lava  has  relieved  the  pressure 
and  thus  removed  the  cause  of  the  shocks  ;  while  in  the  cases 
of  an  opposite  character,  where  the  vibration  still  continued 
after  the  eruption  had  begun,  it  is  reasonable  to  suppose  that 
the  relief  was  only  local,  and  not  sufficient  to  affect  the  whole 
adjacent  region. 

As  before  remarked,  the  curves  indicating  the  number  of  re- 
corded earthquakes  in  all  parts  of  the  world  expand  rapidly  as 
we  approach  the  present  epoch.  There  is  no  reason  to  suppose, 
however,  that  this  means  anything  more  than  that  our  records 
are  growing  every  year  more  complete  :  only  the  observations 
of  the  last  century  and  a  half  can  be  considered  as  making  the 
slightest  claim  to  completeness.  No  inference  can  be  drawn 
at  present,  then,  or  probably  for  a  long  time  to  come,  as  to 
whether  seismic  energy,  as  a  whole,  throughout  the  world,  is 
on  the  increase  or  decrease.  On  this  point  we  shall  be  for  a 
long  time  in  the  dark.  But  the  question  next  arises,  whether 
the  records,  especially  those  of  the  last  two  or  three  centuries, 
exhibit,  when  plotted  in  curves,  any  indication  of  irregular  or 
paroxysmal  energy  ;  that  is,  whether  there  are  certain  epochs 
during  each  century,  when  the  number  and  intensity  of  shocks 
are  greater  than  at  others.  Although  the  dates  are  far  too  in- 
complete to  admit  of  a  perfectly  satisfactory  answer  to  this 
question,  Mr.  Mallet  thinks  he  is  justified  in  asserting  that  there 
are  minor  intervals  of  comparative  repose,  averaging  from  five 
to  ten  years  in  duration,  alternating  with  periods  of  consider- 
ably increased  activity  of  a  year  or  two  in  length.  These 
shorter  intervals  do  not  seem  to  follow  any  regular  law,  so 
far  as  can  be  made  out  from  the  curves  ;  but  they  seem  to  be 
in  connection  with,  periods  of  fewer  earthquakes,  and  usually 
with  the  occurrence  of  less  violent  shocks.  There  are  also 
two  very  well  marked  epochs  of  extreme  violence  and  frequen- 
cy of  earthquakes,  —  one  towards  the  end,  and  one,  still  more 
violent  than  the  other,  about  the  middle  of  each  century.  The 


Earthquakes.  23 

form  of  the  curves  seems  to  indicate  a  comparatively  sudden 
burst  of  seismic  energy  at  each  great  paroxysm,  and  then  a 
more  gradual  subsidence  of  the  action  ;  as  if  the  disturbing 
forces  had  been  of  a  nature  to  reach  rapidly  the  maximum  of 
their  power,  and  then  to  sink  more  slowly  into  their  normal 
condition  of  activity.  Still,  the  data  are  few  for  general  re- 
sults of  much  weight  in  regard  to  long  periods  of  alternate 
repose  and  paroxysmal  energy.  If,  as  Mr.  Mallet  thinks,  such 
conclusions  can  already  be  drawn,  it  is  a  strong  argument  in 
favor  of  considering  earthquake  action  to  be  connected  with 
some  great  general  cause,  commensurate,  in  the  magnitude  of 
the  area  in  which  it  acts,  with  that  of  the  earth  itself. 

In  comparing  the  relation  of  earthquakes  to  the  times  of 
the  year  in  which  shocks  have  occurred,  in  order  to  ascertain 
whether  there  are  months  or  seasons  in  which  seismic  energy 
is  more  developed  than  in  others,  quite  interesting  coincident 
results  have  been  obtained  by  all  who  have  occupied  them- 
selves with  these  investigations.  In  the  first  place,  it  is  clear- 
ly made  .out  that  there  are  more  earthquakes,  in  the  northern 
hemisphere,  during  winter  than  summer.  Thus,  Dr.  Kluge 
gives,  for  the  shocks  registered  from  1850  to  1857,  nineteen 
hundred  and  eighty-four  as  occurring  in  the  winter  half  of  \ 
the  year  (September  to  March),  and  only  eighteen  hundred 
and  thirty-four  as  taking  place  in  the  summer  half.  The 
months  in  which  the  smallest  number  of  shocks  took  place 
were  May,  June,  and  July ;  and  October,  December,  and  Feb- 
ruary, those  in  which  the  number  was  greatest.  Mr.  Mallet 
draws  substantially  the  same  results  from  the  comparison  of 
the  curves  of  mensual  seismic  energy  for  the  whole  period  of 
the  catalogue,  or  thirty-two  centuries.  In  the  northern  hemi- 
sphere he  finds  the  annual  paroxysmal  minimum  to  occur 
in  July,  and  the  maximum  in  January,  while  the  preponder- 
ance of  winter  over  summer  in  the  number  of  shocks  is  very 
decided.  The  results  of  observation  in  the  southern  hemi- 
sphere agree  with  those  in  the  northern,  the  frequency  of  i 
earthquakes  there  being  greater  in  summer  (our  winter)  than 
in  winter  (our  summer)  ;  but  the  observations  are  so  limited 
in  number,  and  the  area  is  so  much  more  extensively  covered 
by  water,  that  at  present  any  deductions  of  this  kind  in  regard 


24  Earthquakes. 

to  the  southern  hemisphere  have  much  less  weight  than  the 
similar  ones  for  the  northern.  The  same  results  are  shown 
when  the  months  are  grouped  into  four  seasons,  —  the  curves 
showing  clearly  a  maximum  for  the  three  winter  months,  and 
a  minimum  for  the  summer. 

Another  coincidence  appears  to  have  been  pretty  clearly  in- 
dicated, if  not  positively  made  out,  by  the  labors  of  Messrs. 
Mallet  and  Perrey :  namely,  the  occurrence  of  a  maximum  of 
4-7  earthquake  shocks  about  the  time  of  the  winter  solstice,  and  a 
minimum  at  the  autumnal  equinox.  And  there  is  still  another 
branch  of  inquiry  with  reference  to  the  frequency  and  violence 
of  earthquakes,  which  is  of  great  interest,  although  as  yet  by 
no  means  thoroughly  worked  out :  that  is,  the  action  of  the 
moon  on  the  earth,  or  the  connection  between  the  phases  of 
the  moon  and  the  recurrence  of  shocks.  The  coincidence  of 
certain  great  earthquakes  with  extreme  high  or  low  tide  had 
been  repeatedly  noticed  in  South  America  many  years  ago,  and 
the  probable  influence  of  the  moon  on  the  interior  of  the  earth 
asserted  by  different  scientific  authorities.  Baglivi,  an  Italian 
author,  in  his  description  of  the  Roman  earthquake  of  1703, 
published  in  1737,  notices  particularly  the  fact  of  the  more 
common  occurrence  of  earthquakes  at  the  time  of  full  moon. 
M.  Perrey  was  the  first,  however,  to  enter  into  the  labo- 
rious calculations  necessary  to  throw  further  light  on  this 
question  of  so  much  interest ;  and  although  it  cannot  be  con- 
sidered as  thoroughly  settled,  still  the  facts  seem  to  indi- 
cate that  the  action  of  the  moon,  or  of  the  sun  and  moon 
combined,  is  really  perceptible  in  increasing  the  number 
and  violence  of  earthquakes  at  certain  periods.  M.  Perrey's 
results,  as  obtained  from  a  combination  of  the  observations  of 
1844  -  47,  are  as  follows  :  First,  that  earthquakes  occur  more 
frequently  at  the  Syzygies  than  at  the  Quadratures  ;  secondly, 
that  they  also  are  more  numerous  at  the  Perigees  than  at  the 
Apogees ;  and,  finally,  that,  whenever  a  disturbance  is  going 
on,  the  frequency  of  the  shocks  is  increased  by  the  passage  of 
the  moon  over  the  meridian  of  the  place  in  question.  These  re- 
sults would  indicate  that  the  moon  has  an  action  on  the  interior 
of  the  earth  somewhat  analogous  to  that  which  it  exerts  on 
the  ocean,  —  the  time  of  greatest  frequency  of  shocks  agreeing 


Earthquakes.  25 

with  that  of  the  highest  and  lowest  tides.  The  great  interest  of 
this  investigation  will  be  easily  understood,  since  it  bears  very 
directly  on  one  of  the  most  vexed  questions  of  modern  geological 
science,  namely,  whether  the  interior  of  the  earth  is  really  in  a 
liquid  state,  or  sufficiently  so  to  admit  of  its  yielding  to  the 
attraction  of  the  sun  and  moon  in  such  a  degree  as  to  produce 
a  sensible  result,  as  would  be  the  case,  provided  it  could  be 
clearly  proved  that  the  supposed  lunar  influence  on  the  fre- 
quency cff  earthquakes  really  existed.  Such  an  investigation, 
moreover,  has  an  important  bearing  on  many  points  of  theo- 
retical geology,  and  it  will  certainly  not  be  dropped  until  the 
question  has  been  definitely  settled.  Of  M.  Perrey's  conclu- 
sions Mr.  Mallet  says,  that  they  rest  upon  so  narrow  a  basis 
of  induction  that  they  must  be  accepted  with  caution  ;  yet  he 
admits  that  they  possess  more  than  sufficient  probability,  from 
physical  considerations,  to  induce  further  inquiry.  The  Com- 
mittee of  the  French  Academy  of  Sciences  to  which  M.  Per- 
rey's  conclusions  were  referred  were  evidently  much  impressed 
with  the  character  of  his  results,  although  cautious  in  accepting 
them,  until  they  should  be  confirmed  by  the  reduction  of  future 
observations,  or  by  going  back  and  computing  a  still  greater 
number  of  older  ones. 

However  important  the  relative  frequency  of  earthquakes,  as 
compared  with  the  positions  of  the  sun  and  moon,  may  be  to 
the  scientific  man,  as  having  a  profound  theoretical  significance, 
people  generally  are  much  more  interested  in  the  connection 
of  seismic  with  meteorological  phenomena.  A  great  many 
persons  think  that  they  remember  some  peculiarities  of  the 
weather  as  having  preceded  any  great  shock ;  and  in  almost 
every  earthquake-shaken  region  there  are  popular  theories  as 
to  the  premonitory  symptoms  of  these  disturbances, — although 
these  are  very  different  in  different  places.  The  most  common 
one  is,  perhaps,  that  oppressive  heat,  accompanied  by  unusual 
stillness  of  the  atmosphere  and  a  light  mist,  is  a  sure  forerun- 
ner of  a  shock.  In  accordance  with  this  theory,  the  inhab- 
itants of  San  Francisco  were  greatly  excited,  last  September, 
by  the  occurrence  of  a  remarkably  smoky  appearance  in  the 
atmosphere  during  several  days  ;  and  a  report  having  been  set 
afloat  that  an  uncommonly  high  tidal  wave  had  been  experienced 


26  Earthquakes. 

in  the  harbor,  the  city  became  wild  with  excitement.  Nothing 
unusual  happened,  however,  and  the  smoke  was  afterwards 
traced  to  burning  forests  far  north  on  the  coast.  The  most 
careful  comparison  of  the  catalogues  of  earthquake  occurren- 
ces with  registers  of  the  weather  has  failed  to  reveal  any  sub- 
stantial reason  for  supposing  that  any  of  these  peculiar  indi- 
cations really  do  precede  the  shocks.  Only  this  much  appears 
probable  :  that  a  great  depression  of  the  barometer,  implying 
a  diminution  of  the  pressure  of  the  atmosphere  on  ftie  earth, 
may  be  in  some  cases  the  determining  cause  of  an  earthquake. 
This,  as  we  can  easily  conceive,  might  be  the  case ;  since,  if  we 
suppose  the  normal  condition  of  the  crust  of  the  earth  in  an 
habitually  disturbed  region  to  be  that  of  a  nicely  balanced 
equilibrium  between  the  internal  forces  seeking  exit,  or  relief 
by  change  of  place,  and  the  pressure  of  the  overlying  material, 
gravity  and  tenacity  acting  against  expansion,  it  is  not  un- 
reasonable to  admit  that  a  stidden  depression  of  the  barome- 
ter, perhaps  to  the  amount  of  two  and  a  half  inches,  equal  to 
one  twelfth  the  whole  weight  of  the  atmosphere,  may  turn  the 
scale,  so  that  the  crust  shall  give  way  and  the  pent-up  forces 
find  relief,  giving  us  the  evidence  of  it  in  a  vibration  of  the 
superincumbent  strata.  There  are  many  facts  which  seem  to 
indicate  that  the  severe  storms,  gales  of  wind,  and  heavy 
rains,  which  have  repeatedly  been  observed  to  occur  simul- 
taneously with  earthquake  shocks,  and  which,  from  meteoro- 
logical causes,  are  preceded  by  a  remarkable  fall  of  the  ba- 
rometer, are  thus  causally  connected  with  seismic  disturbances. 
The  depression  of  the  mercurial  column  indicates  a  change  in 
the  currents  of  the  atmosphere,  which  will  result  in  a  violent 
storm,  and  the  diminished  pressure  of  the  atmosphere  is  the 
direct  agent  in  starting  the  vibration,  which  takes  place  sooner 
than  it  would  have  happened,  had  it  not  been  for  this  disturb- 
ing element. 

Many  curious  statements  have  been  made  with  regard  to  the 
presentiments  of  approaching  earthquakes  manifested  by  dif- 
ferent animals,  some  of  which  seem  well  authenticated,  while 
others  must  be  set  down  as  the  results  of  excited  imaginations. 
Some  of  the  peculiar  actions  ascribed  to  animals  may  easily  be 
accounted  for  by  the  emission  of  carbonic  acid  or  other  gases 


Earthquakes.  27 

from  the  ground,  which  is  known  to  accompany  some  earth- 
quakes in  volcanic  regions,  and  which  might  be  perceptible  to 
animals  whose  sense  of  smell  or  nervous  susceptibility  was 
more  delicate  than  our  own.  Dogs  are  supposed  to  be  pecu- 
liarly sensitive  in  this  respect,  and  hogs  and  geese  are  relieved 
to  show  fear  of  approaching  volcanic  disturbances  sooner  than 
other  animals.  Birds  generally  are  very  quick  at  taking  alarm, 
as  might  naturally  be  expected  from  their  delicate  organiza- 
tion. AH  incidents  recorded  with  regard  to  the  behavior  of 
animals,  before  and  during  earthquake  shocks,  must  be  taken 
with  many  grains  of  allowance  ;  but  such  as  are  well  authenti- 
cated are  extremely  interesting,  as  indicating  differences  be- 
tween the  nervous  susceptibilities  of  man  and  the  lower  ani- 
mals. 

Whether  there  is  any  relation  between  earthquake  phenom- 
ena and  the  magnetism  of  the  earth  is  a  question  which  has 
been  frequently  discussed,  and  for  the  satisfactory  answering 
of  which  the  data  are  not  yet  sufficient.  We  know  no  reason 
why  there  should  be  any  real  connection  between  the  disturb- 
ances of  the  earth's  crust  and  the  magnetic  currents  which 
circle  around  it,  nor  has  any  been  proved.  On  the  contrary, 
most,  if  not  all,  of  the  investigators  in  this  branch  consider 
that  there  is  no  reason  to  believe  that  the  unusual  vibrations 
of  the  magnetic  instruments,  which  have  been  sometimes  ob- 
served in  earthquakes,  are  anything  more  than  the  mechani- 
cal result  of  the  motions  of  the  earth's  crust. 

We  have  now  gone  rapidly  over  most  of  the  ground  which 
has  been  occupied  by  compilers  of  earthquake  catalogues,  and 
given  a  sketch  of  the  principal  results.  It  must  be  remem- 
bered, however,  that  a  large  portion  of  the  data  used  are  en- 
tirely wanting  in  the  elements  of  scientific  accuracy,  and  that 
in  consequence  of  this  looseness  of  statement  only  conclusions 
of  the  most  general  character  could  be  drawn  from  them.  So 
impressed  was  Mr.  Mallet  with  this  fact,  that  he  thus  expressed 
himself  at  the  end  of  the  Report  to  the  British  Association 
which  had  occupied  him  for  so  many  years.  He  says :  "  In 
conclusion,  I  would  repeat  my  conviction  that  a  farther  expen- 
diture of  labor  in  earthquake  catalogues,  of  the  character  hith- 
erto compiled,  and  alone  possible  from  the  data  to  have  been 


28  Earthquakes. 

compiled,  is  now  a  waste  of  scientific  time  and  labor.  The 
main  work  presented  for  seismologists  in  the  immediate 
future  must  consist  in  good  observations,  with  seismometers 
advantageously  placed  at  sufficiently  distant  stations,  and  gal- 
vanicalty  connected  as  to  time, — and  in  the  careful  observation 
of  the  traces  left  by  great  shocks  (when  of  recent  occurrence) 
upon  buildings,  and  other  objects,  artificial  and  natural,  with  a 
view  to  determining  the  nature  of  the  forces  that  have  affected 
them,-  aided  by  the  resources  of  the  physicist  and  the  mathe- 
matician." 

Just  about  the  time  the  above-quoted  conclusions  of  Mr. 
Mallet  were  put  upon  paper,  there  occurred  the  great  earth- 
quake of  December,  1857,  which  shook  a  large  part  of  the 
Neapolitan  territory,  and  was  the  third  in  extent  and  severity 
of  all  those  of  which  there  is  any  record  as  having  occurred  in 
Europe,  —  since  more  than  ten  thousand  persons  were  killed 
by  it,  and  a  great  number  of  towns  and  villages  were  almost 
destroyed.  Immediately  after  this  calamity,  Mr.  Mallet  applied 
to  the  Royal  Society  of  London  for  a  small  grant  of  money,  to 
pay  a  part  of  the  expense  of  visiting  the  locality,  and  making  a 
thorough  investigation  of  all  the  facts  in  the  light  of  the  most  re- 
cent seismological  inquiries.  The  request  was  acceded  to,  and 
Mr.  Mallet  travelled  carefully  over  the  shaken  region  during 
several  months,  and  was  afterwards  employed  for  nearly  two 
years  in  preparing  his  report,  the  title  of  which  stands  at  the 
head  of  this  article.  This  report  was  published  in  1862,  the 
Royal  Society  contributing  three  hundred  pounds  towards  the 
expense.  It  fills  two  royal  octavo  volumes,  and  is  most  elab- 
orately and  beautifully  illustrated,  in  a  manner  worthy  of  the 
first  really  thorough  investigation  in  the  department  of  Seis- 
mology. 

It  is  hardly  necessary  to  state  that  one  investigation  has  not 
exhausted  the  subject ;  it  has  rather  set  the  example  of  what 
ought  to  be  done  for  many  earthquakes  ;  and  it  is  especially  of 
value,  as  leading  the  way  in  a  new  line  of  research,  and  as 
showing  what  can  and  must  be  done  in  order  to  arrive  at  as 
complete  a  knowledge  as  possible  of  the  workings  of  the  mys- 
terious agencies  by  which  these  great  convulsions  are  brought 
about.  Some  of  the  more  important  results  obtained  by  Mr. 
Mallet  in  regard  to  the  Neapolitan  earthquake  may  here  be 


Earthquakes.  29 

given,  as  a  specimen  of  the  kind  of  material  which  will  have  to 
be  accumulated  from  all  quarters  of  the  globe  before  the  de- 
mands of  scientific  accuracy  shall  have  been  satisfied. 

In  the  first  place,  in  the  map  accompanying  the  report  in 
question,  the  regions  in  which  the  shock  was  equally  intense 
are  designated  by  curves,  called  isoseismal  curves ;  then  the 
whole  of  the  wave-paths,  or  lines  of  direction  in  which  the 
shocks  were  propagated  at  each  locality,  are  marked  by  red 
lines.  These  wave-paths  of  course  radiate  from  the  focal  point 
of  the  shock,  and  so  carefully  were  they  determined,  chiefly  by 
observations  of  the  position  of  fallen  buildings,  and  the  charac- 
ter of  the  movements  and  fractures  in  those  left  standing,  that 
sixteen  of  these  lines,  when  protracted  back,  pass  through  the 
same  focal  point,  or  within  a  circle  of  five  hundred  yards 
radius  around  it,  while  thirty-two  more  fall  within  a  circle  con- 
centric with  the  former  and  of  one  mile  radius.  Now,  theo- 
retically, the  intersection  of  any  two  wave-paths  is  sufficient  to 
fix  the  position  of  the  "  seismic  vertical,"  or  the  point  on  the 
earth's  surface  vertically  above  the  spot  where  the  impulse  or 
shock  originated.  The  evidence,  then,  in  this  case  was  ample 
for  determining  this  point  as  accurately  as  possible ;  since,  what- 
ever be  the  nature  of  the  impulsive  force,  or  however  it  may 
operate,  the  wave  of  impulse,  as  propagated  outwardly,  passes 
simultaneously,  or  almost  so,  from  points  about  the  actual 
focus  at  a  considerable  distance  from  each  other,  —  the  point 
from  which  the  disturbance  starts  not  being,  by  any  means,  a 
mathematical  one.  The  position  of  the  point  on  the  surface 
vertically  over  the  seismic  focus  was  found,  as  above,  to  be  / 
near  Caggiano,  a  village  sixty  miles  a  little  south  of  east  from 
Naples. 

The  next  important  question  to  be  settled  was  the  depth  of 
this  focus  below  the  surface,  —  a  point  of  great  interest,  as  will 
be  perceived  at  once,  in  its  connection  with  the  theory  of  earth- 
quake action.  This  depth  can  easily  be  obtained  by  mathe- 
matical calculation,  when  the  distance  on  the  surface  from 
any  station  to  the  seismic  vertical  is  known,  together  with  the 
angle  of  emergence  of  the  wave-path,  the  seismic  vertical  being 
another  wave-path,  and  the  point  of  convergence  of  the  two 
being  the  focus  from  which  the  wave  started.  Of  course  the 
limits  of  error  are  considerable  in  an  investigation  of  this  kind ; 


30  Earthquakes. 

but  the  results,  as  graphically  exhibited  on  Mr.  Mallet's  dia- 
gram, are  quite  as  satisfactory  in  their  agreement  as  could  be 
expected.  Out  of  twenty-six  separate  wave-paths,  twenty-three 
start  from  the  seismic  vertical  at  a  depth  of  above  7-|  miles  ; 
the  maximum  depth  is  8^  miles,  and  the  minimum  2|  miles.* 
Eighteen  of  the  wave-paths  start  from  the  seismic  vertical 
within  a  vertical  range  of  twelve  thousand  feet,  and  having  a 
mean  focal  depth  of  5|  miles,  which  may  be  taken  as  the  depth 
of  the  focus.  Here  is  an  extremely  important  numerical  re- 
sult, and  similar  results  from  other  regions  are  highly  desir- 
able for  comparison  with  this. 

It  will  be  impossible  here  to  enter  into  the  detail  of  the 
other  numerical  results  obtained  by  Mr.  Mallet,  —  the  posi- 
tion and  depth  of  the  focal  centre  being,  of  course,  the  most 
important,  and  having  been  determined  in  this  instance  for 
the  first  time  with  any  approach  to  accuracy.  Other  interest- 
ing points  discussed  in  the  summing  up  of  the  results  of  the 
investigation  are  :  the  form  of  the  isoseismal  areas,  —  that  is, 
of  the  regions  over  which  the  shock  was  felt  with  equal  inten- 
sity ;  the  relations  of  this  area  to  the  focal  depth  ;  the  effects 
of  the  physical  configuration  of  the  surface  and  the  geological 
structure  of  the  region  on  the  progress  of  the  wave  ;  the  proofs 
of  reflection  and  refraction  of  the  shock  by  a  range  of  moun- 
tains standing  in  the  way,  including  reasons  why  certain  areas 
escaped  entirely  ;  the  form,  position,  and  dimensions  of  the  focal 
cavity ;  the  amplitude  and  velocity  of  the  wave,  both  on  the  sur- 
face and  in  the  wave-paths  ;  the  velocity  with  which  the  shock 
started,  and  its  gradual  dying  out ;  the  relation  of  the  seismic 
foci  of  the  Italian  Peninsula,  and  the  general  relations  of  the 
seismic  bands  of  the  Mediterranean  basin.  To  give  even  a 
synopsis  of  the  results  obtained  under  the  above  heads  will 
not  be  possible  here ;  those  who  desire  to  investigate  seismic 
phenomena  must  consult  the  volumes  themselves. 

We  see  that  Mr.  Mallet  was  fully  justified  in  demanding 
more  thoroughly  scientific  observations  than  those  we  had  pre- 
viously to  his  work,  and  that  he  has  given  a  most  excellent 
example  of  how  such  investigations  should  be  made.  He  has 
shown  that  we  can  not  only  learn  much  from  the  application 

*  These  results  are  given  in  geographical  miles,  of  sixty  to  a  degree. 


Earthquakes.  31 

of  seismological  inquiries  to  future  earthquake  shocks,  but 
that  we  have  it  in  our  power,  to  a  certain  degree,  to  recover  the 
history  of  the  past,  by  investigating  the  results  of  former  con- 
vulsions as  registered  in  the  buildings  fissured  or  in  the  ruins 
of  those  overthrown  by  ancient  earthquakes. 

Among  the  practical  results  of  investigations  like  those  of 
Mr.  Mallet,  there  are  none  so  interesting  to  the  public  at  large, 
especially  to  persons  living  in  earthquake  regions,  as  those 
which  relate  to  the  proper  methods  of  structure  for  safe  houses 
and  other  edifices  in  countries  liable  to  these  disturbances. 

This  experienced  observer  expresses  his  strong  conviction, 
"  that  the  evils  of  the  earthquake,  like  all  others  incident  to 
man's  estate,  maybe  diminished,  or  even  multiplied,  by  the  ex- 
ercise of  his  informed  faculties  and  energies,  and  by  his  appli- 
cation of  forethought  and  knowledge  to  subjugate  this,  as  every 
other  apparent  evil  of  his  estate,  by  skill  and  labor."  He  fur- 
ther adds,  in  reference  to  this  important  question :  "  Were 
understanding  and  skill  applied  to  the  future  construction  of 
houses  and  cities  in  Southern  Italy,  few,  if  any,  human  lives 
need  ever  again  be  lost  by  earthquakes,  which  there  must 
recur,  in  their  times  and  seasons." 

What  is  true  of  Southern  Italy  should  also  be  true  of  the 
Pacific  coast  of  our  own  territory,  a  region  liable  to  severe 
shocks,  and  yet  where  we  hope  to  see  populous  States  develop 
themselves  in  wealth,  intelligence,  and  security  to  life.  The 
prevailing  tone  in  that  region,  at  present,  is  that  of  assumed 
indifference  to  the  dangecs  of  earthquake  calamities,  —  the 
author  of  a  voluminous  work  on  California,  recently  published 
in  San  Francisco,  even  going  so  far  as  to  speak  of  earthquakes 
as  "  harmless  disturbances."  But  earthquakes  are  not  to  be 
"  bluffed  off."  They  will  come,  and  will  do  a  great  deal  of 
damage.  The  question  is,  How  far  can  science  mitigate  the 
attendant  evils,  and  thus  do  something  towards  giving  that 
feeling  of  security  which  is  necessary  for  the  full  develop- 
ment of  that  part  of  the  country  ? 

There  has  repeatedly  been  talk  at  San  Francisco  of  estab- 
lishing an  astronomical  observatory,  either  by  itself  or  in  con- 
nection with  the  State  university.  If  the  people  of  California 
are  wise,  and  have  money  to  give  for  scientific  research,  let 


32  Earthquakes. 

them  found  a  physical,  and  not  an  astronomical,  observatory. 
We  have  enough  of  the  latter  already,  ill-equipped,  and  in  the 
majority  of  cases  not  manned  at  all.  Quite  a  sufficient  num- 
ber of  large  telescopes  are  rusting  on  their  piers  in  various 
parts  of  the  country,  as  valueless  for  all  real  scientific  results 
as  if  they  never  had  been  taken  from  the  boxes  in  which  they 
were  imported.  Let  California  take  warning  from  these,  and 
remember  that  a  very  large  endowment  is  necessary  for  the 
perm'anent  maintenance  of  an  astronomical  observatory,  and 
that,  if  not  permanently  maintained,  in  the  hands  of  an  able 
astronomer,  with  the  means  of  paying  his  assistants  and  of 
publishing  his  results,  it  will  be  nothing  but  an  expensive 
toy.  Besides,  the  climate  of  California  and  the  climatological 
conditions  are  ill-suited  to  astronomical  work  in  a  fixed  obser- 
vatory. The  fogs  of  San  Francisco,  and  the  dust  of  the  interior, 
will  be  found  alike  unfavorable  to  'the  successful  prosecution 
of  this  branch  of  scientific  research.  A  physical  observatory, 
on  the  contrary,  which  need  not  necessarily  be  a  permanency, 
having  as  its  principal  object  the  investigation  of  the  seismo- 
logical  phenomena  occurring  en  the  Pacific  coast,  would,  if 
properly  managed,  furnish  results  of  exceeding  value,  not  only 
as  contributions  to  an  important  branch  of  science  hitherto 
much  neglected,  but  as  having  a  practical  bearing  on  the  wel- 
fare of  the  people  and  the  development  of  the  State,  the  value 
of  which  can  hardly  be  overestimated.  In  no  portion  of  the 
world  is  there  a  better  chance  for  an  establishment  having  in 
view  the  thorough  investigation  pf  earthquake  phenomena. 
The  great  plain  of  the  Sacramento  and  the  San  Joaquin  should 
for  a  time  be  connected  with  San  Francisco  galvanically,  by 
wires  proceeding  from  the  branch  observatories  at  properly 
selected  localities.  Seismometers  of  the  most  approved  con- 
struction should  be  set  up,  and  their  records  compared  with 
the  other  results  of  every  important  shock,  as  shown  in  the 
effect  on  buildings  and  on  the  surface  of  the  ground,  and  in  all 
the  other  methods  of  which  Mr.  Mallet's  book  furnishes  so 
excellent  a  model. 

Of  Herr  Yolger's  volume  and  theory  something  may  be  said 
at  another  time,  in  discussing  the  various  theories  of  the  nature 
of  the  forces  involved  in  the  phenomena  of  volcanoes  and 
earthquakes. 


VOLCANOES. 


1.  Vesuvius.    By  JOHN  PHILLIPS,  M.  A.    Oxford.    1869.    12mo. 

2.  Histoire    Complete  de   la  grande  Eruption  de    Vesuve   de 
1631.     Par  H.  LE  HON.     Bruxelles.     1866.     8vo. 

3.  Reise  der  Oesterreichischen  Fregatle  Novara  urn  die  Erde  in 
den  Jahren  1857,  1858,  1859.     Geologischer  Theil,  Erster 
Band,  Erste  Abtheilung,  Geologie  von  Neu-Seeland.     Von 
DR.  FERDINAND  VON  HOCHSTETTER.    Wien.     1864.    4to. 

4.  Voyage  Geologique  dans  les  Republiques  de  Guatemala  et 
San  Salvador.    Par  MM.  A.  DOLLFUS  et  E.  DE  MONT-SERRAT. 
Paris.     1868.     4to. 

5.  The  Natural  System  of  the  Volcanic  Rocks.     By  BARON  F. 
RICHTHOFEN.     Extracted  from  the  Memoirs  of  the  California 
Academy  of  Sciences.     San  Francisco.     1868.     Pamphlet. 

WE  have  placed  at  the  head  of  this  article  the  titles  of  a 
few  of  the  many  volumes  devoted  chiefly  to  the  subject  of 
volcanoes  which  have  issued  from  the  press  during  the  past 
few  years.  To  give  a  complete  list  of  the  volumes  and  papers 
in  which  the  phenomena  of  volcanism  have  been  described 
and  discussed,  even  if  only  the  productions  of  the  last  five 
years  were  to  be  included  in  it,  would  require  many  pages. 
On  the  subject  of  the  volcanic  island  of  Santorin  alone,  at 
least  six  different  works  were  published  during  the  year  1868. 
One  author,  Le  Hon,  gave,  in  1866,  a  complete  history  of  an 
eruption  of  Vesuvius  which  took  place  two  hundred  and  thirty- 
eight  years  ago ;  while  several  other  writers,  some  of  them 
known  as  geological  authors  and  others  not*,  have  taken  ad- 
vantage of  the  recent  period  of  activity  of  that  interesting 
volcano  to  serve  up  portions  of  the  mass  of  the  old  material 
in  a  new  form,  adding  in  some  cases  new  facts  of  value  to  the 
previously  existing  stock,  but  generally  relying  for  their  chances 
3 


34  Volcanoes. 

of  success  rather  on  elegance  of  typography,  or  other  extrinsic 
circumstances,  than  on  scientific  accuracy  or  originality  of  ideas. 
The  reason  of  the  exceptional  activity  in  this  department  of 
book-making  is  partly  that  the  volcanoes  themselves  —  at 
least  several  of  those  best  known  —  have  been  unusually  ac- 
tive, and  partly  because  the  fashion  of  illustrated  and  sen- 
sational books  on  scientific  subjects  has  been  set,  and  of  all 
the  subjects  which  geology  presents  there  is  none  which  so 
excites  the  popular  mind  as  the  phenomena  of  volcanoes  and 
earthquakes. 

Earthquakes  are  events  simply  fearful ;  there  is  nothing 
about  them  which  is  not  appalling  in  its  nature.  They  come 
without  warning,  and  leave  nothing  but  dismay  and  ruin  be- 
hind. Even  the  minor  shocks  are  terrible,  and  more  alarming 
in  proportion  to  the  number  of  times  they  have  been  experi- 
enced. It  is  only  in  California  that  an  attempt  has  been  made 
to  pooh-pooh  an  earthquake  ;  but  even  there  the  hollowness  of 
the  derision  was  but  too  evident.  In  an  earthquake-shaken 
country  the  time  that  elapses  between  the  instant  when  one 
perceives  that  an  earthquake  wave  is  approaching  and  that 
when  its  first  effect  is  felt  is  one  into  which  a  thousand  appre- 
hensions can  be  crowded.  Then,  if  ever,  one  feels  the  utter 
insignificance  of  man  as  an  integral  part  of  creation.  The 
blow  may  fall  lightly  and  leave  no  sensible  trace  behind  ;  or, 
on  the  other  hand,  it  may  crush  and  overwhelm.  The  regu- 
lating screws  of  the  horrid  machinery  are  invisible.  There 
is  no  reason  why  one  should  await  with  more  calmness  the 
approach  of  an  earthquake  shock  than,  with  his  head  on  the 
anvil,  the  falling  of  a  steam-hammer,  not  knowing  beforehand 
at  what  point  the  ponderous  mass  is  to  be  arrested  by  the 
engineer  in  charge  of  the  machine. 

Volcanoes,  on  the  other  hand,  give  in  almost  all  cases  some 
previous  warnings  of  their  intention  to  change  their  usual  qui- 
escent state  for  one  of  destructive  activity.  Their  disastrous 
effects  can  often  -be  to  a  large  extent  avoided  by  flight.  It  is 
only  very  rarely  that  an  eruption  is  so  sudden  and  violent  as  to 
overwhelm  and  destroy  without  previous  and  oft-repeated  warn- 
ings. Again,  eruptive  volcanic  action  is  usually  prolonged 
over  many  days  or  weeks,  or  even  months,  and  the  phenomena 


Volcanoes.  35 

exhibited  are  usually  —  if  the  eruption  is  on  a  large  scale  —  of 
surpassing  grandeur,  from  a  picturesque  as  well  as  from  a  sci- 
entific point  of  view.  Perhaps  there  is  no  scene  offered  by  any 
play  of  nature's  forces  so  wonderfully  attractive  as  that  of  a 
great  volcanic  eruption,  especially  when  seen  by  night.  The 
combination  of  every  conceivable  element  of  the  picturesque 
and  the  sublime  afforded  by  the  great  outbreaks  of  Kilauea, 
as  reported  by  the  few  who  have  had  the  good  luck  to  wit- 
ness some  of  thejn,  may  be  mentioned  as  an  instance  in 
poini 

No  wonder,  then,  that  the  subject  of  volcanoes  has  always 
been  an  attractive  one  to  the  "general,  as  well  as  to  the  sci- 
entific, traveller  and  writer,  and  that  such  a  great  num- 
ber of  volumes  have  been  published,  and  are  still  publishing, 
treating  either  of  volcanoes  in  general  or  of  particular  erup- 
tions or  periods  of  eruptive  activity.  The  work  of  the  veteran 
Oxford  professor,  John  Phillips,  the  title  of  which  is  placed  at 
the  head  of  the  list  preceding  this  article,  is  one  of  the  most 
noticeable  of  those  possessing  a  somewhat  popular  character. 
Within  the  limits  of  three  hundred  and  fifty  pages  it  gives  a 
succinct  history  of  Vesuvius  and  of  the  adjacent  volcanic  re- 
gion so  much  visited  by  travellers,  and  is  on  all  points  exact 
and  clear.  The  illustrations  of  the  volume  are  numerous  and 
effective,  although  not  elaborate,  and  very  far  from  sensa- 
tional. The  book  is  exactly  what  was  desirable  as  a  guide 
to  travellers  of  scientific  tastes,  and  may  be  consulted  with 
profit  and  pleasure  by  the  professional  geologist.  It  contains, 
besides,  a  catalogue  of  Vesuvian  minerals.  There  is  also  a 
chapter  devoted  to  the  theory  of  "volcanic  excitement,"  —  a 
subject  on  which  much  has  been  written,  especially  of  late, 
but  in  regard  to  which  it  must  be  admitted  that  we  have  still 
much  to  learn. 

The  work  of  M.  Le  Hon,  placed  second  on  our  list,  is  es- 
pecially valuable  as  containing  a  large  map,  which  appears  to 
have  been  carefully  constructed,  and  which  exhibits  all  the 
flows  of  lava  from  Vesuvius  between  the  years  1631  and  1861. 
This  is  the  only  map  which  professes  to  give  with  any  approach 
to  exactness  the  position  of  these  masses,  and  evidently  it 
.  could  not  have  been  produced  without  considerable  labor  and 


36  Volcanoes. 

without  numerous  excavations.  The  description  of  the  erup- 
tion of  1631  is  carefully  compiled,  and  gives  a  good  idea  of 
this  the  most  devastating  of  all  the  modern  outbreaks  of  Vesu- 
vius. By  this  eruption  it  is  probable  that  at  least  four  thou- 
sand persons  lost  their  lives  in  various  ways,  while  more 
than  forty  towns  and  villages  were  destroyed,  the  pecuniary 
losses  being  estimated  at  twenty  millions  of  ducats,  —  an  enor- 
mous sum  at  that  time. 

The  volcanic  phenomena  of  a  far  distant  but  exceedingly  in- 
teresting region  —  New  Zealand  —  are  brought  to  our  notice 
for  the  first  time  in  a  comprehensive  manner  by  Dr.  Hochstet- 
ter,  in  two  separate  works,  —  one,  in  royal  8vo  form,  of  a  popu- 
lar character,  entitled  simply  "  Neu-Seeland  "  ;  the  otber,  a  vol- 
ume of  the  series  published  by  the  Austrian  government  as  the 
official  account  of  the  voyage  of  the  frigate  Novara,  made  in 
the  years  1857  -  59.  The  first-mentioned  work  was  published  by 
Cotta,  in  1863,  with  every  luxury  of  adornment,  and  is  one  of  the 
most  attractive  books  —  half  scientific  and  half  narrative — ever 
issued.  The  quarto  official  volume  is  also  beautifully  printed 
and  illustrated,  and  is  largely  devoted  to  a  description  of  the 
New  Zealand  volcanoes,  as  well  as  of  the  wonderful  geysers,  hot- 
springs,  and  solfataras  which  form  so  peculiar  and  attractive  a 
feature  of  the  island,  and  which  are  admirably  represented  in 
the  chromo-steel  plates  of  the  popular  volume  and  the  chromo- 
lithographs of  the  other.  These  indicate  a  type  of  geological 
scenery  resembling  that  of  the  geysers  of  Iceland,  but  on  a 
grander  scale,  and  with  the  peculiar  added  beauty  of  a  won- 
derfully interesting  and  abundant  vegetation.  Dr.  Hochstet- 
ter's  books  are  rich  in  information  about  a  new  and  remarkable 
region,  but  they  are  very  little  encumbered  with  generalities 
or  theoretical  views. 

Almost  equally  magnificent  in  its  typography  and  style  of 
publication  is  the  work  placed  fourth  on  our  list,  —  an  official 
publication  of  the  French  government,  issued  from  the  Im- 
primerie  Imperials,  as  an  instalment  of  the  results  of  the 
scientific  mission  instituted  by  the  Emperor  for  exploring 
Mexico  at  the  time  when  his  unfortunate  military  expedition 
to  that  country  was  planned.  In  carrying  out  this  explora- 
tion, MM.  Dollfus  and  Mont-Serrat  —  neither  of  them  a  geolo- 


Volcanoes.  37 

gist  of  reputation  —  spent  a  little  over  two  years  in  that  region, 
eight  months  of  it  in  Central  America.  The  results  of  their 
investigations  have  been  laid  before  the  public  in  the  form  of  a 
ponderous  quarto,  in  which,  as  in  many  other  works  of  French 
savans  which  treat  of  the  geology  of  parts  of  our  continent, 
there  is  but  little  that  is  new,  while,  on  the  other  hand,  it  con- 
tains many  blunders.  The  Emperor  has  been  unfortunate  in 
the  representatives  of  geological  science  whom  he  has  sent 
to  the  American  continent.  M.  Laur,  who  visited  California 
some  ten  years  ago,  and  made  a  report  on  its  mines,  showed  a 
remarkable  tact  for  misapprehending  the  plainest  and  most 
important  facts,  and  drawing  erroneous  conclusions ;  as,  for 
instance,  when  he  announced  that  the  yield  of  the  Comstock 
Lode  would  never  exceed  three  millions  of  dollars  a  year, 
whereas,  in  reality,  it  soon  after  reached  twelve  millions.  About 
half  of  the  volume  of  MM.  Dollfus  and  Mont-Serrat  is  taken 
up  with  remarks  on  the  volcanoes  of  Central  America,  and  it 
is  astonishing  how  little  there  is  of  original  and  valuable  mat- 
ter to  be  found  in  it.  One  is  more  annoyed  still,  on  exam- 
ining the  beautifully  engraved  illustrations,  to  find  that  they 
bear  evident  marks  of  the  sensational  style  ;  the  slopes  of  the 
cones  are  all  enormously  exaggerated,  and  no  data  are  given  by 
which  these  errors  can  be  corrected.  A  few  simple  outlines 
plotted  from  actual  measurements  would  have  been  worth  more 
than  the  whole  dozen  and  a  half  of  costly  steel  plates  which 
are  given,  the  style  of  which  takes  us  back  to  the  dark  ages 
of  the  illustrations  to  Humboldt's  "  New  Spain.5*  One  should 
compare  them  with  the  drawings  and  sections  illustrating  M, 
Hartung's  books  on  the  Azores,  Madeira,  and  Porto  Santo,  to 
see  the  difference  between  fancy  and  real  work. 

Baron  Richthofen's  quarto  pamphlet  of  a  little  less  than  a 
hundred  pages,  with  no  illustrations,  is  entirely  different  from 
most  of  the  works  already  cited,  since  it  addresses  itself  exclu- 
sively to  the  professional  geologist.  It  is  the  result  of  long 
observation  and  of  much  study  bestowed  011  the  volcanic  rocks 
by  an  able  and  experienced  observer  in  different  parts  of  the 
world.  In  it  many  of  the  most  difficult  points  in  the  theory  of 
volcanoes  are  discussed  in  such  a  manner  as  to  make  its  study 
imperative  on  all  who  desire  to  form  an  original  opinion  in 


38  Volcanoes. 

regard  to  the  subjects  with  which  it  deals.  We  shall  refer  to 
it  further  on,  or  at  a  future  time,  when  the  theory  of  volcanoes 
and  earthquakes  is  under  discussion. 

In  a  previous  article  we  endeavored  to  give  a  systematic 
view  of  the  present  condition  of  our  knowledge  of  earthquake 
phenomena,  so  far  as  their  external  manifestations  are  con- 
cerned. We  discussed  the  data  of  the  earthquake  catalogues 
with  reference  to  the  geographical  distribution  of  seismic  areas, 
to  the  relations  of  time  of  earthquake  shocks,  and  to  their  con- 
nection with  movements  and  conditions  of  the  atmosphere. 
We  had  occasion  to  refer  more  than  once  to  the  relations 
between  volcanoes  and  earthquakes  both  in  time  and  space, 
and  thus  prepared  the  way  for  a  discussion  of  the  causes  of 
these  truly  wonderful  and  most  closely  connected  phenomena. 

Before  entering  on  this  discussion,  however,  we  must  become 
more  fully  acquainted  with  the  facts  concerning  volcanoes,  and 
it  is  with,  these  that  this  article  will  be  occupied,  leaving  for  a 
third  and  final  one  of  the  series  an  attempt  to  show  how  far 
science  is  able,  at  the  present  day,  to  throw  light  on  those 
workings  of  unseen  forces  which  are  manifested  in  the  earth- 
quake shock,  the  volcanic  eruption,  the  rising  and  falling  of  the 
land,  and  the  formation  of  mountain  chains,  —  for  all  these  are 
effects  of  one  and  the  same  cause,  or,  at  least,  of  one  set  of 
causes  so  intimately  allied  with  each  other  that  the  discussion 
of  any  one  of  them  must  necessarily  include  that  of  all  the 
others. 

In  pursuance  of  this  plan,  then,  we  purpose,  in  this  article,  to 
give  an  outline  of  what  is  known  in  regard  to  volcanoes,  having 
reference  chiefly  to  their  external  manifestations,  such  as  form, 
geographical  distribution,  and  their  different  phases  of  repose 
and  action.  This  will  prepare  the  way  for  us  to  get  some  idea 
of  the  nature  of  the  forces  at  work  below  ;  for  a  volcano  is  a 
sort  of  happy  accident,  which  lets  us  into  some  of  nature's 
secrets,  —  a  peep-hole  through  which  we  may  get  a  glimpse  of  the 
interior  of  the  earth.  It  is  evident  that,  if  a  great  smelting 
establishment  were  buried  so  that  no  part  of  it  should  be  visible 
except  the  top  of  the  tall  chimney,  from  which  gases-were  issu- 
ing, and  some  piles  of  slags  accumulated  on  the  outside,  and  we 
had  to  report  on  the  nature  of  the  processes  going  on  below 


Volcanoes.  39 

from  these  imperfect  data,  the  investigation  would  require  no 
little  scientific  knowledge  and  ingenuity,  and  probably  some 
time  would  elapse  before  a  guess  could  be  hazarded  as  to  the 
character  of  the  work  of  which  these  gaseous  exhalations  and 
slags  were  the  only  tangible  result.  So  it  is  with  volcanoes  : 
we  collect  and  analyze  their  products,  whether  solid,  fluid,  or 
gaseous ;  we  note  the  times  and  places  of  these  manifestations 
of  the  internal  forces  and  their  correlations  with  other  natural 
phenomena ;  we  avail  ourselves  of  every  conceivable  source  of 
information  touching  the  subject,  and  reason  to  the  best  of  our 
ability  on  the  whole  mass  of  evidence  thus  obtained.  And 
yet  the  result,  it  must  be  confessed,  is  far  from  satisfactory. 
There  are  many  obscure  points  in  the  theory  of  volcanoes  and  « 
earthquakes  ;  and  if  the  general  cause  of  the  phenomena  of 
volcanism  is  in  the  opinion  of  most  geologists  correctly  deter- 
mined, yet  in  regard  to  the  precise  mode  of* operation  of  the 
internal  forces  there  is  great  discrepancy  of  opinion,  even 
among  those  who  have  devoted  most  time  to  this  branch  of  in- 
quiry. 

A  volcano  is  a  mountain,  hill,  or  area  of  the  earth's  surface, 
connected  with  some  more  or  less  deeply  seated  portion  of  the 
interior  by  a  canal  or  passage,  through  which  solid  or  gaseous 
materials  are  brought  to  the  surface.  It  is  almost  invariably 
the  case  that  the  substances  thus  ejected  are  intensely  hot, 
the  rocky  material  often  pouring  forth  in  a  condition  of  igneous 
fluidity,  and  the  term  "  lava  "  is  applied  to  anything  which  has 
flowed  in  this  way  and  which  in  cooling  consolidates  into  rock. 
Elevations  which  would,  according  to1  the  definition  just  given, 
be  included  under  the  head  of  volcanoes,  but  which  emit  only 
water  with  paroxysmal  violence,  are  usually  called  "  geysers. " 
These  are*rare  and  on  a  small  scale  as  compared  with  proper 
volcanoes.  Orifices  from  which  mud  is  thrown  out,  called 
"  mud-volcanoes,"  are  not  uncommon,  but  are  usually  of  small 
dimensions,  and  the  temperature  of  the  substances  they  eject  is 
in  many  instances  raised  but  little  above  their  ordinary  tem- 
perature. 

Volcanoes  are  called  "  active  "  if  they  have  within  a  com- 
paratively recent  period  given  indications  of  eruptive  action. 
The  term  "  dormant "  may  be  used  to  designate  that  peculiar 


40  Volcanoes. 

condition  when  the  internal  forces  have  remained  quiet  for  a 
great  length  of  time,  so  that  only  faint  traces  of  activity  are  still 
visible  ;  and  if  all  chemical  action  has  ceased,  and  there  is  no 
record  in  history  of  any  outbreak,  the  volcano  or  volcanic  re- 
gion is  considered  and  called  "  extinct."  Yet  it  is  not  an  easy 
thing  to  draw  the  line  between  dormant  and  extinct  volcanoes. 
Thus  Epomeo,  on  the  island  of  Ischia,  remained  entirely  in- 
active for  seventeen  hundred  years.  So  Vesuvius  was  never 
known  in  history  as  an  active  volcano  until  A.  D.  79.  A  great 
saucer-like  depression,  overgrown  with  wild  grapes,  in  which 
Spartacus  once  camped  with  ten  thousand  men,  marked  the 
position  of  its  crater,  and  Herculaneum  and  Pompeii  were  two 
populous  towns  at  its  base.  By  the  well-known  eruption  of 
that  year,  these  two  towns  were  overwhelmed,  —  greatly  to 
the  inconvenience  of  their  inhabitants,  no  doubt,  but  immensely 
to  our  advantage^  —  the  whole  adjacent  region  devastated,  and 
the  mountain  built  up  into  an  entirely  different  shape  from  that 
which  it  had  had  before.  From  this  time  on,  the  eruptions  con- 
tinued, without  any  long  periods  of  repose  between  them,  until 
the  fourteenth  century,  after  which  there  was  quiet  for  nearly 
three  hundred  years.  During  this  period  of  repose  the  crater 
became  filled  anew  with  a  forest  vegetation,  and  only  a  couple 
of  hot-springs  gave  evidence  of  the  forces  slumbering  beneath. 
All  of  a  sudden,  again,  in  1631,  a  furious  eruption  took  place, 
and  seven  streams  of  lava  flowed  down  the  slopes  of  the  moun- 
tain at  one  time.  Since  that,  Vesuvius  has  almost  always  been 
uneasy,  there  being  rarely  an  interval  of  rest  of  more  than  ten 
years,  and,  of  late,  the  eruptions  have  been  very  violent  and 
frequent.  The  Gunung  Gelungung,  one  of  the  great  volcanoes 
of  Java,  was,  and  had  been  from  time  immemorial,  perfectly 
quiescent,  and  the  site  of  the  present  crater  was  a  broad  valley, 
the  inhabitants  of  which  had  never  dreamed  of  anything  but 
the  most  peaceful  security.  But  suddenly,  in  the  middle  of  a 
fine  day  in  October,  1822,  they  received  notice  to  quit,  in  the 
form  of  a  violent  explosion  beneath  their  feet,  which  proved  to 
be  the  commencement  of  one  of  the  most  fearfully  destructive 
volcanic  eruptions  on  record. 

There  are  but  few  volcanoes  which  are  permanently  active, 
and  those  which  are  thus  in  constant  eruption  are  usually  far 


Volcanoes.  41 

from  violent.  Paroxysmal,  powerful  action  occurs  only  occa- 
sionally, sometimes  recurring,  after  short  intervals,  then  slack- 
ening and  perhaps  ceasing  altogether,  or,  after  a  long  period  of 
'repose,  say  hundreds  or  perhaps  thousands  of  years,  beginning 
again. 

We  have  in  the  moon  the  best  possible  specimen  of  thor- 
oughly played  out  volcanism.  The  most  careful  watching  of  the 
surface  with  powerful  telescopes  seems,  thus  far,  to  have  failed 
to  reveal  any  evidence  of  changes  taking  place  there.  And 
since  there  is  neither  water  nor  air  to  produce  erosion  or 
disintegration  of  the  volcanic  surface,  it  seems  pretty  clear  that 
it  will  remain  as  it  now  is  for  an  indefinite  length  of  time. 

In  dividing  terrestrial  volcanoes  into  extinct,  dormant,  and 
active,  it  must  be  understood,  then,  that  these  terms  are  used 
to  express  our  general  opinion  with  regard  to  their  condition, 
based  on  a  variety  of  circumstances,  and  not  as  indicating  any 
positively  established  criterion  by  which  the  different  classes 
can  be  distinguished  from  each  other.  We  speak  of  the  vol 
came  region  of  Central  France  as  "  extinct,"  because  we  know 
that  a  long  time  has  elapsed  since  any  indications  of  activity 
have  occurred  there ;  this  has  been  ascertained  by  studying 
the  amount  of  erosion  which  has  taken  place  in  the  lava  cur- 
rents and  in  other  ways.  Yet  the  pouring  out  of  a  portion, 
at  least,  of  the  vast  mass  of  volcanic  material  Jjhere  visible 
took  place,  in  all  probability,  after  the  appearance  of  man  on 
the  earth,  although  at  an  epoch  immensely  remote  as  com- 
pared with  historical  time.  Neither  can  any  conclusive  reason 
be  given  why  volcanic  activity  should  not  again  manifest  itself 
in  this  region. 

A  volcano  may  be  considered  as  only  dormant,  and  not  ex- 
tinct, when  in  the  so-called  "  solfataric  condition."  This 
name  is  derived  from  the  Solfatara,  near  Naples,  where  there 
has  been  no  eruption  since  1198,  but  where  vapors  and  gases 
are  constantly  issuing  from  the  region  of  the  old  crater.  These 
vapors  consist  mainly  of  steam,  mixed  to  some  extent  with 
sulphuretted  hydrogen,  and  also  with  sulphurous  acid,  chloro- 
hydric  acid,  carbonic  acid,  and  nitrogen  gases.  The  abun- 
dance of  the  sulphuretted  hydrogen  is  usually  testified  to  by 
the  deposits  of  sulphur,  so  often  met  with  in  the  craters  of  old 


42  Volcanoes. 

volcanoes,  and  undoubtedly  formed  by  the  decomposition  of 
this  gas ;  besides,  the  nose  has  no  difficulty,  if  no  satisfac- 
tion, in  detecting  its  presence.  Steam  and  sulphuretted 
hydrogen  usually  predominate  largely  among  the  products  of 
solfataric  action.  The  other  gases  mentioned  generally,  but 
not  always,  occur  in  smaller  quantity.  Boracic  acid,  petroleum, 
specular  iron,  chlorides  of  the  alkalies,  realgar,  and  orpiment 
are  also  occasionally  observed  among  the  gaseous  emanations  in 
old  volcanic  regions.  Some  observers  testify  to  the  existence 
of  inflammable  gases  in  sufficient  quantities  to  produce  flames, 
these  gases  being  hydrogen  and  sulphuretted  hydrogen;  but 
there  are  other  observers,  equally  distinguished,  who  have  had 
frequent  opportunities  to  examine  volcanoes,  both  in  action  and 
at  rest,  and  who  have  never  seen  any  indication  of  flame.  What 
is  generally  called  fire,  in  eruptions,  is,  of  course,  simply  the 
light  or  the  reflection  of  the  lava,  which  is  intensely  heated 
but  not  actually  undergoing  combustion. 

During  the  solfataric  condition  of  a  volcano,  its  crater  be- 
comes blocked  up  with  congealed  lava,  perhaps  overgrown  with 
forests  and  dense  vegetation,  and  the  signs  of  activity  die  out, 
until,  as  the  last  relic  of  former  life,  only  a  thermal  spring 
may  be  found  here  and  there,  —  an  indication  of  the  mighty 
forces  slumbering  beneath.  Such  is  the  present  condition  of 
nearly  all  the  great  volcanic  cones  on  our  own  coast,  from 
Arizona  to  Oregon. 

Midway  between  the  conditions  of  solfataric  repose  and  of 
paroxysmal  violence  is  another  stage  of  activity,  in  which  some 
volcanoes  remain  during  long  periods,  while  a  few  appear 
never  to  pass  out  of  it  into  more  violent  action ;  others,  how- 
ever, remain  in  this  condition  of  partial  repose  during  the  in- 
tervals between  violent  outbursts.  At  such  times  the  crater 
and  the  channel  connecting  it  with  the  interior  remain  open,  and 
the  lava  can  be  seen  in  them  maintaining  a  mobile  condition, 
while  occasional  explosions  of  the  surface  of  the  melted  mass 
take  place,  fragments  of  slag  and  cinders  being  thrown  up  and 
mostly  falling  back  into  the  abyss  from  which  they  were 
hurled.  This  was  the  condition  of  Vesuvius  when  visited  by 
the  writer  in  November,  1843.  At  that  time  there  had  been 
no  eruption  of  lava  overflowing  the  lip  of  the  crater  since 


Volcanoes.  43 

1839,  when  the  cavity  was  cleaned  out,  and  left  as  a  funnel 
three  hundred  feet  deep,  accessible  to  the  bottom.  From  this 
time  a  smaller  cone  began  to  grow  inside  the  large  one,  and 
in  1843  it  was  about  fifty  feet  high,  and  could  be  reached  by 
clambering  down  the  walls  of  the  old  crater,  the  whole  bottom 
of  which,  around  the  foot  of  the  new  cone,  was  covered  with 
lava,  which  was  red-hot  a  few  inches  beneath  the  surface,  but 
could  in  most  places  be  safely  walked  on.  From  the  vent  a 
shower  of  cinders  was  thrown  up  every  fifteen  or  twenty  min- 
utes ;  and  although  it  was  possible  to  climb  to  the  summit  of 
the  cone  on  the  windward  side,  with  occasional  calls  for  skill 
in  dodging  the  projectiles,  the  orifice  was  too  much  occupied 
with  ascending  vapors  to  permit  of  anything  below  being  clearly 
seen.  This  interior  cone  kept  on  growing  by  additions  made 
to  it  from  the  falling  materials,  and  finally,  in  1847,  the  crater 
became  filled,  and  the  lava  overflowed,  running  down  on  three 
sides  at  once.  From  that  time  forward  Vesuvius  became  very 
uneasy,  and  finally  a  great  eruption  took  place  in  1850.  This 
lasted  about  twenty  days,  and  when  it  was  over  the  summit  of 
the  mountain  was  left  much  changed  in  form,  the  old  walls 
having  been  broken  down,  the  central  cone  .reduced  in  size, 
and  a  new  crater  formed,  about  two  miles  in  circumference,  and 
a  hundred  and  fifty  feet  deep.  The  volcano  then  remained 
quiet  from  1850  to  1855,  when  it  became  very  active ;  again  a 
grand  eruption  occurred  in  1858,  and  slight  ones  in  1860  and 
1861.  Since  the  last-named  year  Vesuvius  has  rarely  been  at 
rest.  During  the  winter  of  1867  -  68  there  was  a  great  out- 
burst of  volcanic  force,  which  lasted  several  months. 

In  the  condition  of  half-repose  just  noticed  as  not  uncommon 
between  intervals  of  paroxysmal  activity,  observers  are  able 
to  look  down  into  the  throat  or  channel  of  Etna,  as  well  as 
of  Stromboli,  during  the  periods  of  repose  between  the  erup- 
tions, which  take  place  with  great  regularity  every  ten  or  fifteen] 
minutes.  At  such  times  the  lava  is  seen  to  move  up  and  down 
in  the  chimney  ;  as  it  rises,  its  surface  swells  up  into  a  great 
blister,  which  finally  gives  way  to  the  tension  exerted  and  ex- 
plodes with  a  loud  noise,  the  fragments  being  scattered  and 
thrown  up  with  great  force  ;  the  column  of  melted  matter  then 
sinks  back  into  temporary  repose,  and  rises  again  after  an  in- 


44  Volcanoes. 

terval  of  a  few  minutes.  The  same  phenomena  were  observed 
on  Sangay,  one  of  the  Quito  group,  a  permanently  half-active 
volcano,  like  Stromboli. 

The  most  gigantic  exhibition  of  this  condition  of  the  volcanic 
forces  is  to  be  seen  in  Kilauea  during  its  quiet  periods,  when 
the  crater,  which  is  three  miles  in  its  greatest  diameter,  has  in 
it  large  pools  of  boiling  and  extremely  fluid  lava,  which  is' con- 
tinually thrown  up  in  jets  of  from  thirty  to  forty  feet  in  height, 
that  fall  back  into  the  pool  before  they  have  time  to  cool. 
These  lakes  of  liquid  fire  vary  in  size  according  as  the  volcano 
is  more  or  less  active,  and  sometimes  cover  the  whole  area  of 
the  crater,  the  wind  raising  the  .surface  in  waves  of  molten 
rock,  which  dash  against  the  encircling  walls  with  an  inde- 
scribably grand  effect.  The  greater  the  liquidity  of  the  lava, 
the  less  the  force  with  which  it  is  thrown  up,  for  the  jets  of 
imprisoned  vapors  do  not  have  time,  in  a  very  fluid  material, 
to  accumulate  sufficient  pressure  to  act  with  extreme  explosive 
violence. 

The  phenomena  which,  we  have  seen,  thus  characterize  the 
semi-active  condition  of  volcanic  activity  are,  in  most  respects, 
similar  to  those  of  the  fully  active  state,  differing  rather  in  the 
degree  of  violence  with  which  they  are  manifested  than  in  kind. 
It  seems,  indeed,  that  the  longer  and  more  complete  the  repose 
of  the  volcano  has  been,  the  more  violent  its  action  when  it 
once  breaks  out  again.  This  is  natural,  for  the  resistance  to 
an  outburst  must,  as  an  ordinary  thing,  go  on  increasing  the 
longer  the  vent  remains  stopped,  and  when  this  resistance  is 
finally  overcome  the  magnitude  of  the  eruption  will  be  propor- 
tionate to  the  force  required  to  clear  the  way.  The  first  re- 
corded eruption  of  Vesuvius  was  the  most  violent  of  any  which 
are  known  to  have  taken  place ;  next  to  this  in  its  destructive 
effects  was  that  of  1631,  occurring,  as  it  did,  after  several  hun- 
dred years  of  entire  repose. 

In  regard  to  the  precursors  of  a  violent  eruption,  or  the 
symptoms  by  which  the  approach  of  one  may  be  detected, 
there  is  much  uncertainty.  It  may  be  said,  however,  that  a 
great  outbreak  is  to  be  expected  when  the  internal  forces  begin 
to  show  signs  of  uneasiness  and  the  usual  phenomena  of  half- 
repose  to  be  intensified  in  their  action.  It  seems  a  well-authen- 


Volcanoes.  45 

ticated  fact,  that  previous  to  an  eruption  of  Vesuvius  the  wells 
and  springs  adjacent  to  the  niountain  begin  to  dry  up.  When 
volcanic  cones  are  covered  with  snow  it  is  not  uncommon  for 
the  eruptions  to  be  preceded  by  devastating  floods,  caused  by 
its  melting,  the  natural  result  of  the  gradual  warming  up  of  the 
mountain  mass. 

The  following  arc  the  ordinary  phenomena  of  violent  erup- 
tions :  an  appearance  of  fire  ;  lightning ;  subterraneous  noises, 
or  thunder ;  ejection  of  ashes,  cinders,  or  blocks  of  lava  ;  the 
pouring  out  of  melted  lava ;  and,  in  connection  with  earth- 
quake shocks,  fissures  in  the  earth  and  permanent  changes  in 
the  level  of  the  adjacent  country.- 

Great  volcanic  paroxysms  are  often  preceded  by  more  or  less 
.violent  earthquake  shocks,  which  are  both  frequent  and  pro- 
longed, but  usually  limited  to  the  mass  of  the  volcano  itself  or 
its  immediate  vicinity.  Tremendous  underground  detonations 
are  heard,  sounding  like  the  firing  of  heavy  cannon  or  repeated 
volleys  of  musketry.  These  sounds  are  heard  at  all  points  at 
the  same  instant  of  time,  showing  that  they  are  propagated 
through  the  crust  of  the  earth  and  also  that  they  come  from 
a  great  distance  beneath  the  surface.  These  explosive  sounds 
have  been  heard  simultaneously  over  areas  of  many  thousand 
square  miles.  Thus  the  noise  of  the  outbreak  of  the  eruption 
of  Temboro,  on  the  island  of  Sumbawa,  was  heard  all  over 
Java,  and  everywhere  supposed  to  come  from  some  point  in 
the  immediate  vicinity.  It  was  distinctly  audible  at  points 
two  thousand  miles  apart.  As  the  shocks  and  sounds  con- 
tinue, people  become  more  and  more  alarmed  and  excited, 
and  imagine  that  they  see  every  kind  of  portent  in  the  sky 
or  in  the  conduct  of  animals.  It  is  generally  thought  that 
an  oppressive  stillness  pervades  the  atmosphere  just  before 
the  moment  of  the  great"  outbreak,  and  that  dogs,  swine,  and 
geese  exhibit  peculiar  indications  of  fear.  •  How  much  reli- 
ance can  be  placed  on  the  statements  of  the  sensitiveness  of 
animals  to  impending  catastrophes,  it  is  not  easy  to  say ;  but 
it  is  evident  that  the  circumstances  of  a  great  eruption  are 
eminently  favorable  to  a  highly  imaginative  condition  of  the 
mental  faculties. 

The  earthquake  shocks  preceding  volcanic  outbreaks  take 


46  Volcanoes. 

place  while  the  internal  conflict  is  going  on  between  the  im- 
prisoned lava,  seeking  to  find  a  vent,  and  the  resistance  of- 
fered by  the  weight  and  tenacity  of  the  superincumbent  crust. 
When  the  internal  pressure  which  seeks  relief  in  bringing  up 
to  the  surface  the  material  on  which  it  is  acting  at  last  has  its 
own  way,  the  explosion  is  tremendous,  the  mass  of  the  volcano 
being  shaken  to  its  very  foundations.  As  soon  as  the  channel 
of  communication  with  the  interior  is  opened,  which  channel 
usually  communicates  with  the  bottom  of  the  old  crater,  al- 
though not  unfrequently  opened  through  some  new  side  fissure, 
the  pent-up  vapors  and  gases  begin  to  escape  with  tremendous 
force,  carrying  up  in  the  air,  torn  into  fragments,  rocky  masses, 
which  then  fall  and  are  thrown  out  again  repeatedly,  and  thus, 
by  friction  against  each  other  or  by  actual  explosion,  through 
sudden  changes  of  temperature,  are  rapidly  reduced  to  powder 
and  carried  off  with  the  gases  or  vapors  which  rise  from  the 
chimney  of  the  crater. 

The  ejection  of  vapor  and  ashes,  as  the  comminuted  frag- 
ments of  lava  are  called,  is  thus  described  by  Scrope,  who  was 
an  eye-witness  of  one  of  the  grandest  eruptions  of  Vesuvius,  — 
that  of  1822.  He  says :  "  The  rise  of  the  vapor  produces  the 
appearance  of  a  column  several  thousand  feet  high,  based  on 
the  edges  of  the  crater,  and  appearing  from  a  distance  to  con- 
sist of  a  mass  of  innumerable  globular  clouds  of  extreme  white- 
ness, resembling  vast  balls  of  cotton  rolling  one  over  the  other 
as  they  ascend,  impelled  by  the  pressure  of  fresh  supplies  in- 
cessantly urged  upwards  by  the  continued  explosions.  At  a 
certain  height  this  column  dilates  horizontally,  and  —  unless 
driven  in  any  particular  direction  by  aerial  currents  —  spreads 
on  all  sides  into  a  dark  and  turbid  circular  cloud.  In  very 
favorable  atmospheric  circumstances,  the  cloud  with  the  sup- 
porting column  has  the  figure  of  an  immense  umbrella,  or  of 
the  Italian  pine,  to  which  Pliny  the  younger  compared  that  of 
the  eruption  of  Vesuvius  in  A.  D.  79,  and  which  was  accurately 
reproduced  in  October,  1822.  Strongly  contrasting  with  this 
pillar  of  white  vapor-puffs  is  seen  a  continued  jet  of  black 
cinders,  stones,  and  ashes,  the  larger  and  heavier  fragments 
falling  back  visibly  after  describing  a  parabolic  curve.  This 
jet  of  solid  fragmentary  matter  often  reaches  a  height  of  several 


Volcanoes.  47 

thousand  feet,  while  the  vapor  pillar  rises  still  higher.  Forked 
lightnings  of  great  vividness  and  beauty  are  continually  darted 
from  different  parts  of  the  cloud,  but  principally  its  borders. 
The  continual  increase  of  the  overhanging  cloud  soon  hides  the 
light  of  day  from  the  districts  situated  below  it,  and  the  grad- 
ual precipitation  of  the  sand  and  ashes  it  contains  contributes 
to  envelop  the  atmosphere  in  gloom,  and  adds  to  the  conster- 
nation of  the  inhabitants  of  the  vicinity.'' 

If  the  volcano  is  one  which  emits  lava,  this  rises  gradually 
in  the  crater  and  finally  overflows  it  at  the  lowest  point,  unless 
it  succeeds  in  forcing  its  way  through  some  side  fissure.  The 
molten  mass  finds  its  way  down  the  declivity  with  a  rapidity 
proportioned  to  its  fluidity,  overwhelming  and  destroying  every- 
thing which  it  encounters.  Clouds  of  vapor  rise  from  the  flow- 
ing mass,  visible  during  the  day,  the  exterior  soon  becoming 
covered  with  a  dark  crust  of  scoria,  occasional  fissures  in 
which  reveal,  especially  at  night,  the  presence  of  the  intensely 
ignited  material  beneath.  The  flow  of  lava  from  the  volcanic 
vent  indicates  that  the  crisis  of  the  disturbance  is  passed,  and 
that  there  will  thenceforth  be  a  gradual  slackening  in  the 
violence  of  the  eruptive  action. 

Not  a  few  volcanoes,  however,  never  send  out  lava,  but  only 
ashes  and  cinders ;  these  are  usually  the  very  large  ones,  as, 
for  instance,  the  great  cones  of  South  America.  It  is  also  true 
that  large  volcanoes  are  less  frequently  than  smaller  ones 
the  seat  of  great  disturbances.  The  frequency  of  the  eruption 
seems  to  be,  in  a  measure,  in  inverse  proportion  to  the  height 
of  tl)e  volcanic  cones  from  which  they  proceed.  Thus  the  lofty 
volcanoes  of  South  America  have  rarely  had  more  than  one 
eruption  each  in  a  century ;  the  Peak  of  Teneriffe  had  only 
three  between  1430  and  1798.  This  is  very  natural,  since  the 
higher  the  cone  the  greater  the  resistance  offered  to  an  out- 
break by  the  weight  of  the  column.  But  the  rule  is  not  of 
universal  application.  Closely  connected  with  the  last-men- 
tioned fact  is  another,  previously  suggested,  namely,  that  the 
most  fearful  eruptions  may  be  expected  to  occur  after  long  in- 
tervals of  repose.  Both  circumstances  indicate  very  clearly  the 
accumulation  of  force  necessary  to  overcome  increased  resist- 
ance. 


48  Volcanoes. 

At  night  the  column  of  vafpor  arid  ejected  solid  material  ap- 
pears red,  not  because  it  is  actually  a  column  of  flame,  but 
partly  because  it  is  illuminated  by  the  reflection  from  the  red- 
hot  lava  below,  and  also  because  the  fragments  carried  up  in  it 
are  themselves  intensely  heated.  The  fact  that  the  column  re- 
mains perpendicular  all  the  time  is  a  proof  that  it  is  not  a 
flame,  for,  if  that  were  the  case,  it  would  be  swayed  by  the 
wind ;  but  one  of  the  most  characteristic  features  of  an  erup- 
tion is,  that  the  pillar  of  fire  seems  to  stand  immovable  amid 
the  "  wreck  of  matter  "  around  it. 

The  electrical  phenomena  of  a  great  eruption  are  extremely 
interesting.  The  upward  rush  of  heated  vapor  gives  rise  to 
furious  disturbances  in  the  condition  of  the  atmosphere,  as  is 
also  the  case,  on  a  small  scale,  when  steam  escapes  from  an 
ordinary  boiler  through  the  safety-valve.  A  constant  play  of 
lightning  goes  on  around  the  ascending  column,  and  the  noise 
of  the  thunder  is  mingled  with  the  crash  of  the  projected  frag- 
ments of  rock.  Tremendous  bursts  of  rain,  or  even  hail,  often 
occur  at  the  same  time,  and  from  the  same  cause,  —  namely, 
the  electrical  disturbance  of  the  atmosphere,  —  and  the  effect 
of  the  torrents  of  water  rushing  down  the  sides  of  the  volcano 
is  often  more  devastating  than  that  of  the  lava  itself. 

The  mass  of  ashes,  scoriae,  or  cinders  thrown  out  in  some 
volcanic  eruptions  is  prodigious.  In  that  of  Vesuvius,  in  1794, 
four  cones  were  formed  on  a  fissure  nearly  half  a  mile  long, 
each  with  its  separate  crater,  throwing  up  showers  of  red- 
hot  cinders  in  such  rapid  succession  as  to  appear  like  one 
continuous  sheet  of  fire  in  the  air.  These  showers  really 
consisted  of  semi-fluid  lava,  which  expanded  in  the  air  like 
soft  paste.  This  continued  for  several  days,  so  that  the  whole 
space  above  the  crater  seemed  to  be  filled  with  the  frag- 
ments, which  formed  a  column  a  mile  in  circumference  and 
rose  to  an  immense  height,  then  spread  out,  and  seemed  to 
cover  a  much  greater  area  than  the  base  of  the  mountain  itself. 
Generally,  however,  these  ejections  of  cinders  are  intermittent 
.  in  character,  sometimes  following  each  other  in  rapid  puffs,  at 
others  occurring  as  a  succession  of  explosions  at  longer  inter- 
vals. 

The  size  of  the  fragments  thus  ejected  is  variable ;  often  they 


Volcanoes.  49 

are  as  fine  as  the  finest  dust,  but  sometimes  the  lava  is  thrown 
out  in  great  masses.  Thus  Cotopaxi  vomited  forth,  in  1533, 
blocks  of  rock  ten  feet  or  more  in  diameter.  The  so-called 
volcanic  bombs  shelled  out  by  Vesuvius  are  usually  from  the 
size  of  the  fist  to  that  of  the  head.  Generally  they  are  irregu- 
larly rounded  or  pear-shaped ;  but  in  volcanoes  in  which  the 
lava  is  very  liquid  it  comes  down  in  masses  which  flatten 
out  into  cakes  when  they  strike  the  ground.  The  finer  frag- 
ments which  in  prodigious  quantity  accompany  the  .larger, 
and  usually  vary  from  the  size  of  a  pea  to  that  of  a  walnut,  are 
now  almost  everywhere  known  by  the  Italian  name  of  lapilli,  or 
rapilli.  The  finer,  sand-like  material  is  called  puzzolana,  and 
the  finest  of  all  ceneri,  or  ashes. 

One  of  the  most  curious  features  of  the  eruptions  of  some 
volcanoes  is  the  prodigious  number  of  small '  but  perfectly 
formed  crystals  which  are  thrown  out  among  the  materials 
shot  up  from  below.  Vesuvius,  which  is  a  perfect  treasure- 
chambejpof  interesting  minerals,  —  while  most  of  the  American 
volcanoes  are  miserably  provided  in  this  way, — has  furnished  at 
times  showers  of  beautiful  crystals  of  augite,  leucite,  mica,  and 
black  garnet,  the  first-named  being  the  most  abundant.  They 
seem  to  have  existed  ready  formed  in  the  semi-fluid  lava,  or 
else  to  have  crystallized  out  suddenly  at  the  moment  of  its, 
solidification ;  which  of  these  suppositions  is  the  correct  one 
is  not  thoroughly  settled,  although  the  first  seems  by  far  the 
most  probable. 

Vast  masses  of  volcanic  breccia  occur  in  regions  of  eruptive 
rock,  as  for  instance  in  California,  where  beds  hundreds  of  feet 
in  thickness  are  found  covering  many  square  miles  of  area, 
entirely  made  up  of  angular  fragments  of  lava,  of  all  sizes, 
which  have  evidently  been  ejected  in  the  form  in  which  we  now 
see  them.  The  explosions  with  which  volcanic  eruptions  begin 
after  long  periods  of  tranquillity,  and  which  sometimes  pul- 
verize the  whole  summit  of  the  mountain  mass  in  which  they 
occur,  give  rise  to  prodigious  accumulations  of  these  broken 
masses  of  rock.  The  great  eruption  of  Ararat,  in  1840,  was  of 
this  kind,  a  terrific  explosion  having  torn  open  the  side  of  the 
mountain  and  thrown  off  an  immense  mass  of  fragments,  which 
were  projected  for  miles  in  every  direction,  completely  burying 
4 


50  Volcanoes. 

the  town  of  Argure.  There  was  no  eruption  of  lava ;  but  fright- 
ful earthquakes  and  torrents  of  rain  followed,  washing  down  the 
detritus  of  the  explosion  in  immense  floods  of  mud,  which  were 
quite  as  destructive  as  lava  would  have  been. 

According  to  Junghuhn,  the  Javanese  volcanoes  now  emit  no 
lava,  but  only  give  rise  to  streams  of  brecciated  material,  which 
have  issued  from  the  craters  in  that  condition.  The  same  au- 
thor also  gives*  a  most  interesting  account  of  the  great  eruption 
of  Pepandayan,  which  took  place  in  1772.  At  that  time  such  a 
mass  of  fragments  and  blocks  of  lava  was  ejected  that  the  up- 
per part  of  the  Garut  valley,  for  ten  miles  in  length,  was  filled 
with  ashes  and  angular  materials  to  the  average 'depth  of  fifty 
feet,  while  in  places  the  great  blocks  were  heaped  up  in  conical 
hills  as  much  as  a  hundred  feet  in  height.  The  distances  to 
which  such  masses  are  thrown  indicate  the  immensity  of  the 
force  by  which  they  are  hurled  into  the  air.  Cotopaxi,  for 
instance,  in  1583,  threw  rocks  from  eight  to  ten  feet  in  diam- 
eter to  a  distance  of  seven  miles.  The  maximum  tyeight  to 
which  masses  of  lava  have  been  thrown  by  Etna  and  Vesuvius, 
in  different  eruptions,  is  given  by  various  scientific  observers 
as  from  seven  to  ten  thousand  feet. 

Towards  the  end  of  an  eruption  the  ashes  ejected  grow  finer 
and  whiter,  bearing  all  the  marks  of  having  been  longer  sub- 
jected to  the  triturating  process  by  which  the  lava  is  reduced 
to  powder.  This  is  the  -natural  result  of  the  slacking  off  of 
the  ejecting  forces,  the  sinking  down  of  the  column  in  the 
chimney,  and  the  consequent  longer  time  that  the  materials  are 
exposed  to  friction  against  each  other.  Some  observers  have 
thought,  however,  that  the  lava  might  in  many  cases  be  blown 
into  fine  powder  by  the  sudden  expansion  into  steam  of  the 
water  it  contained,  at  the  moment  the  pressure  was  removed 
by  its  issuing  from  the  crater,  and  there  are  some  appearances 
which  seem  to  render  this  view  a  probable  one. 

The  finer  the  ashes  thus  ejected,  the  farther  away  from 
the  volcano  they  fall.  Carried  by  the  wind,  they  are  some- 
times spread  over  vast  areas  of  country,  and  the  exceeding 
fineness  of  the  material  is  testified  to  by  the  slowness  with 
which  it  descends,  sometimes  filling  the  air  so  completely 
that  the  darkness  of  night  reigns  for  days  in  succession.  It  is 


Volcanoes.  51 

stated  that,  in  the  great  eruption  which  devastated  the  island 
of  St.  Vincent  in  1812,  the  fall  of  ashes  on  the  island  of  Bar- 
badoes,  nearly  a  hundred  miles  distant,  caused  so  profound  an  , 
obscurity  that  a  white  handkerchief  was  invisible  at  five  inches] 
from  the  eye.  The  fall  of  ashes  in  the  great  eruption  of  Tem- 
boro,  in  Sumbawa,  in  1815,  produced  so  dense  a  cloud  that  it 
was  dark  as  night  over  the  islands  of  Java  and  Celebes.  Ashes 
fell  on  the  islands  of  Sumatra,  Banda,  and  Amboyna.  West 
of  Sumatra  a  layer  of  lapilli,  two  feet  in  thickness,  floated  on 
the  sea,  so  that  ships  had  difficulty  in  forcing  their  way  through. 
A  careful  comparison  of  all  the  data,  by  Zollinger,  led  him  to 
the  conclusion  that  the  ashes  fell  over  an  area  of  nearly  one  mil- 
lion of  square  miles,  and  that  fully  fifty  cubic  miles  of  material 
was  ejected  in  this  one  eruption.  Junghuhn,  also,  calculated 
the  volume  of  the  ejected  materials  of  the  same  eruption  to  be 
one  hundred  and  eighty-five  times  the  dimensions  of  Vesuvius,  j 
The  area  over  which  daylight  was  shut  off  by  this  fall  of  ashes 
was  nine  hundred  by  seven  hundred  miles  in  extent,  —  that  is,  -" 
equal  to  the  whole  space  in  our  own  territory  between  the 
Mississippi  River  and  the  Atlantic  Ocean.  Coseguina,  in  1835, 
covered  with  its  falling  ashes  an  'area  of  nearly  one  thousand 
two  hundred  miles  in  diameter. 

The  destructive  effects  of  these  showers  of  ashes  are  fear- 
fully increased  by  the  torrents  of  rain  which  frequently  fall  in 
connection  with  great  eruptions ;  these  carry  down  the  ejected 
materials  in  the  form  of  great  flows  of  mud,  which  descend 
the  steep  slopes  with  such  velocity  that  they  cannot  be  avoided, 
and  of  course  completely  overwhelm  everything  they  reach. 
It  was  by  such  a  lava  cPacqua,  or  water-lava,  as  the  Nea- 
politans call  it,  that  Herculaneum  and  Pompeii  were  submerged 
and  destroyed.  For  eight  days  and  nights  the  torrents  of 
mud  poured  down  over  those  ill-fated  towns,  accumulating  in 
places  to  the  depth  of  over  a  hundred  feet.  It  was  the  re- 
markable way  in  which  these  cities  were  overwhelmed  that  has 
preserved  them  so  wonderfully  for  the  inspection  of  people  for 
almost  two  thousand  years.  There  is  no  other  possible  man- 
ner in  which  they  could  have  been  thus  hermetically  sealed  up, 
as  it  were,  all  the  walls  remaining  standing,  and  everything  in 
its  place.  Had  a  shower  of  ashes,  for  instance,  fallen  from 


52  Volcanoes. 

/'  above,  all  the  buildings  would  have  been  crushed  in ;  but  the 
insidious  mud-flow  crept  into  everything,  filling  rooms,  and  even 
-  cellars,  so  gradually  that  nothing  was  disturbed  or  displaced. 
Herculaneum  was  afterwards  covered  with  a  layer  of  solid  lava, 
and  then  built  upon,  so  that  the  opening  of  that  town  has  been 
much  slower  and  more  expensive ;  although,  in  proportion  to 
the  amount  of  space  uncovered,  more  interesting  and  valuable 
works  of  art  have  been  disinterred  than  in  Pompeii. 

When  these  showers  of  ashes  fall  into  the  ocean,  they  grad- 
ually sink  to  the  bottom,  where  they  must  eventually  become 
consolidated  into  rock,  which  may  be  raised  again  to  the  sur- 
face in  the  course  of  the  changes  which  are  continually  going 
on  in  the  relative  positions  of  sea  and  land.  Thus  are  formed 
very  extensive  masses  of  stratified  rock,  which  are  at  the  same 
time  both  eruptive  and  sedimentary,  or  Pluto-Neptunean,  as 
they  have  sometimes  been  called,  as  belonging  to  the  two  do- 
mains of  the  mythological  rulers  of  the  realms  of  fire  and  water. 

It  is  by  the  constant  addition  made  to  their  exterior  by  the 
falling  masses  of  lava,  ashes,  and  lapilli,  that  the  cones  of  vol- 
canoes are  built  up,  —  not  only  the  dominating  one  of  each  vol- 
cano, but  the  secondary  or  minor  ones',  which  are  sometimes 
very  numerous.  These  smaller  cones  form  on  the  fissures 
which  open  frequently  in  the  main  cone,  and  which  connect 
with  the  seat  of  action  in  the  chimney  of  the  volcano,  just  as 
that  is  connected  with  a  still  larger  eruptive  mass  deep  in  the 
interior  of  the  earth.  Etna  has  more  than  seven  hundred  of 
these  smaller  cones  around  its  base,  some  of  which  attain 
respectable  dimensions,  one  reaching  seven  hundred  feet  in 
height,  and  another  four  hundred  or  more.  On  Vesuvius  a 
fissure  opened,  in  1794,  about  nine  hundred  feet  below  the 
summit ;  this  was  two  thirds  of  a  mile  in  length,  and  eight 
new  craters,  with  cones  of  scoriae,  were  formed  upon  it. 

Besides  ashes  and  scoriaB,  we  expect,  in  most  volcanic  erup- 
tions, to  see  rock  rendered  fluid  by  heat  issuing  from  the  crater, 
and  it  is  to  this  molten  rock  that  the  name  of  lava  is  properly 
applied.  The  volcanic  bombs,  lapilli,  and  ashes  are  of  course 
not  fluid  when  ejected,  although  some  of  the  "larger  masses 
sometimes  reach  the  ground  in  a  semi-plastic  condition,  so  as 
to  flatten  themselves  out  into  a  sort  of  cake,  as  before  men- 


Volcanoes.  53 

tioned.  Different  volcanoes  and  volcanic  regions  differ  greatly 
in  respect  to  the  fluidity  of  their  ejections.  Those  of  Java,  for 
instance,  do  not  now  throw  out  any  molten  lava,  but  only 
breccia,  cinders,  and  ashes.  The  Hawaiian  volcanoes,  on  the 
other  hand,  seem  never  to  have  ejected  anything  but  lava  of  a 
high  degree  of  fluidity.  Vesuvius  and  Etna  furnish  both  fluid 
and  solid  materials  in  abundance. 

As  a  general  rule,  the  very  lofty  cones  do  not  emit  cur- 
rents of  molten  lava.  Thus  the  great  South  American  vol- 
canoes throw  out,  almost  exclusively,  cinders  and  ashes.  It 
may  be  stated  that,  in  by  far  the  larger  number  of  instances, 
the  great  masses  of  lava  which  exist  have  come  from  low  vol- 
canoes, or  still  oftener  from  great  fissures  without  any  cones  at 
all,  in  the  form  of  "  massive  eruptions,"  as  they  are  called,  in 
which  form,  probably,  by  far  the  larger  portions  of  the  older 
volcanic  rocks  have  come  to  the  surface. 

It  is  easy  to  see  why,  in  lofty  volcanoes,  the  lava  should 
seek  and  find  in  many  cases  an  issue  at  some  point  far  below 
the  summit.  The  higher  the  column,  the  greater  the  hydro- 
static pressure,  and  when  the  resistance  offered  by  this  exceeds 
that  which  the  sides  of  the  mountain  can  oppose  to  it,  the  latter 
must  give  way,  and  the  lava  find  a  vent  at  the  lowest  available 
point.  The  constant  battering  of  the  internal  walls  of  the 
chimney,  kept  up  by  the  explosive  forces  within,  gradually 
destroys  the  cohesive  power  of  the  material,  breaks  it  up  into 
fragments,  or  threads  it  in  every  direction  with  cracks,  so  that 
it  finally  yields  to  the  repeated  shocks,  just  as  a  piece  of  artil- 
lery fired  with  very  heavy  charges  becomes  at  last  too  weak  to 
resist  any  longer,  and  bursts  into  pieces.  It  is  in  this  way  that 
the  fissures  originate  and  become  filled  with  molten  lava,  which 
solidifies  in  them,  forming  the  dikes  which  are  so  common  in 
volcanic  masses,  and  which  are  so  beautifully  displayed  in 
Etna,  where  its  internal  structure  is  revealed  by  the  great  cut 
into  its  heart  called  the  Val  del  Bove. 

The  flow  of  lava,  in  volcanic  eruptions,  takes  place  in  very 
"different  ways,  according  to  its  consistency  and  the  position  of 
the  point  from  which  it  issues.  In  general  the  crater  fills  up 
gradually,  until  the  fiery  liquid  rises  high  enough  to  pour  over 
the  edge  at  the  lowest  point,  when  it  runs  down  the  slope  with 


54  Volcanoes. 

a  degree  of  rapidity  proportioned  to  its  fluidity.  The  Yesuvian 
lava  is  usually  very  thick  and  ropy.  One  of  the  greatest 
currents  of  that  volcano,  —  that  of  1794,  —  which  was  over  a 
thousand  feet  broad  and  from  twenty  to  thirty  deep,  ran  two 
and  a  half  miles  in  six  hours,  or  at  the  rate  of  2,160  feet  in  an 
hour.  The  lava  of  Mauna  Loa,on  the  other  hand,  is  so  liquid, 
that  when  it  issues  from  the  crater  it  pours  down  the  steep 
slope  of  the  mountain,  sometimes  with  amazing  velocity. 
Thus  Mr.  Coan  says  of  the  eruption  of  1855 :  "  In  one  place 
only  we  saw  the  river  [of  lava]  uncovered  for  thirty  rods,  and 
rushing  down  a  declivity  of  from  ten  to  twenty-five  degrees. 
The  scene  was  awful,  and  the  momentum  incredible.  The 
f  fusion  was  perfect,  and  the  velocity  forty  miles  an  hour." 
This  lava,  in  making  its  way  down  the  mountain-side,  leaps 
over  precipices  in  literal  cascades  of  fire,  presenting  a  most 
sublime  spectacle.  It  occasionally  forces  its  way  out  from  a 
side  fissure,  —  under  immense  pressure  of  course,  —  when  it 
plays  as  a  fountain,  and  the  'jets  of  liquid  fire  are  reported  by 
trustworthy  authorities  as  rising  sometimes  to  the  height  of 
six  hundred  or  eight  hundred  feet. 

Lava  streams,  however  fluid  the  material  may  be,  soon  be- 
come covered,  as  they  run  down  the  sides  of  the  volcano,  with 
a  consolidated  crust.  This  hardened  surface  gradually  thick- 
ens, and  the  bottom  and  sides  also  become  more  or  less  con- 
gealed, so  that  the  flow  continues  through  a  sort  of  tunnel,  as 
if  it  were  being  poured  out  of  a  sack  made  of  its  own  substance. 
The  surface  gets  broken  up  into  great  angular  masses,  which, 
by  the  motion  beneath,  are  thrown  into  disorder  and  piled  up 
on  each  other,  as  cakes  of  ice  are  on  the  sudden  breaking  up  of 
one  of  our  great  rivers, —  the  St.  Lawrence  for  instance.  In 
the  great  eruption  of  .Mauna  Loa,  already  mentioned,  the  lava 
made  its  way  seventy  miles  reckoned  by  the  course  of  its  flow, 
and  forty  in  a  direct  line,  to  Hilo ;  and  after  its  surface  had 
become  quite  hard  all  the  way,  and  there  was  no  evidence  of 
activity  visible  except  the  columns  of  vapor  ascending  from  its 
head  and  foot,  Mr.  Coan  believed  that  the  interior  was  still* 
moving  downwards.  This  stream  of  lava  was  three  miles  wide 
on  an  average,  and  in  some  places  three  hundred  feet  deep. 
The  masses  of  broken  crust  were  piled  up  on  it  to  the  height 
of  a  hundred  feet  at  various  points. 


Volcanoes.  55 

The  lava  of  Vesuvius  seems  more  variable  in  its  consistency 
than  that  of  almost  any  other  volcano.  In  the  eruption  of 
1805,  the  velocity  with  which  it  issued  from  the  crater  was 
almost  equal  to  that  of  the  Mauna  Loa  current ;  on  the  other 
hand,  the  stream  of  1822,  when  it  reached  Resina,  moved  at 
the  rate  of  only  five  or  six  feet  an  hour.  That  of  1819  was  in 
motion,  at  the  rate  of  three  feet  an  hour,  nine  months  after 
its  issue.  The  rate  of  motion,  measured  by  Dolomien,  of  one 
stream,  was  a  mile  a  year. 

The  low  conducting  power  of  lava  is  the  reason  why  the  inte- 
rior of  the  mass  can  remain  fluid  so  long  and  run  beneath  a 
crust  of  its  own  substance.  The  exterior  hardens,  can  be 
walked  over,  or  perhaps  even  cultivated,  while  the  interior  is 
still  red-hot.  This  internal  heat  lasts  for  a  long  time.  The 
lava  of  Jorullo  was  hot  enough  to  light  a  cigar  twenty-one 
years  after  its  issue  ;  and  sixty-six  years  later  it  was  still  per- 
ceptibly heated,  sufficiently  so  to  give  rise  to  fumaroles.  One 
of  the  lava  flows  of  Etna  —  that  of  1787  —  spread  over  a  mass 
of  snow,  which,  in  1830,  still  remained  under  it  unmelted, 
while  the  overlying  mass  of  rock  was  quite  hot.  The*  snow 
was  preserved  from  melting  by  a  cover  of  ashes,  through  which 
the  heat  was  conducted  with  extreme  slowness. 

The  manner  in  which  volcanoes  are  built  up  by  successive 
ejections  of  ashes,  scorias,  and  lava,  and  the  question  whether 
the  vast  size  of  some  cones  is  due  in  part  to  any  other  cause 
than  this  simple  one  of  the  piling  up  of  erupted  materials 
around  a  central  orifice,  now  remain  to  be  discussed. 

The  simplest  possible  form  of  a  volcanic  accumulation  is  that 
of  the  ordinary  cinder  cone,  built  up  by  a  single  eruption.  Such 
cones  are  among  the  most  common,  as  well  as  the  most  charac- 
teristic, features  of  almost  every  volcanic  district.  The  coarse 
fragments  thrown  out  heap  themselves  around  the  orifice  as 
they  fall,  in  the  form  of  a  circular  bank,  which,  as  the  eruptive 
action  continues,  increases  in  size  until  it  becomes  a  hill,  hav- 
ing the  form  of  a  truncated  cone,  with  a  funnel-shaped  hollow 
at  the  summit.  A  section  of  one  will  show  that  they  are 
rudely  stratified,  and  that  the  inclination  of  the  strata  decreases 
with  the  distance  from  the  centre.  These  cones  are  of  all  sizes, 
from  that  of  a  hay-cock  to  that  of  a  mountain.  The  "  Puys," 


56  Volcanoes.  » 

as  they  are  called,  of  Central  France,  —  Auvergne,  Velay,  and 
the  Vivarais,  —  are  hills  of  scoria?  thrown  up  in  this  way. 
Near  Clermont-Ferrand  there  are  above  sixty  cones  strung 
together  on  a  line  more  than  sixty  miles  in  length,  and  the  fis- 
sure on  which  these  were  built  up  is  continued  in  Velay  and 
the  Yivarais,  with  two  hundred  or  more  such  cones  arranged 
in  a  belt  twenty  miles  long.  The  shape  of  these  accumulations 
of  ejected  materials  varies  with  the  conditions  under  which 
they  are  formed.  When  the  wind  blows  steadily  from  one 
quarter,  the  materials  will  be  more  heaped  up  on  one  side, 
and  this  effect  is  very  marked  in  the  region  of  the  trade-winds. 
A  great  many  causes  may  be  effective  in  modifying  the  cones 
thus  formed.  One  is  the  issuing  from  them  of  a  current  of 
lava,  by  which  the  mass  is  broken  down  on  one  side  ;  such 
breached  cones  are  among  the  most  common  features  of  many 
volcanic  regions. 

An  ordinary  cone  resulting  from  a  single  eruption  consists, 
then,  of  a  pile  of  scoria?,  lapilli,  and  other  loose  materials,  with 
a  single  current  of  lava,  which  may  have  flowed  from  the  sum- 
mit, the  side,  or  the  base  of  the  elevation,  and  which  will  be 
found  spreading  itself  out  over  the  adjacent  region  in  a  sheet  or 
stream,  proportioned  in  size  to  the  extent  of  the  eruption  and  the 
nature  of  the  surface  over  which  it  has  found  room  to  extend  it- 
self. The  result  of  repeated  eruptions  occurring  from  the  same 
vent  will  be  the  gradual  building  up  of  a  mass,  which  grows  in 
size  constantly,  but  has  the  same  .kind  of  structure  from  top  to 
bottom.  Beds  of  solid  lava  alternate  in  it  with  others  of  frag- 
mentary materials,  and  the  whole  system  dips  in  all  directions 
from  the  centre.  It  is  not  to  be  supposed,  however,  that  any 
one  of  the  beds  of  lava  entirely  surrounds  the  cone ;  on  the 
contrary,  if  a  horizontal  section  were  made  through  such  an 
accumulation,  it  would  be  seen  that  each  outflow  of  molten 
rock  has  only  added  to  the  mass  a  portion  of  a  concentric  belt, 
so  that  the  cone  is  built  up  by  gradual  additions  of  ejected  ma- 
terials, first  on  one  side  and  then  on  another.  Besides,  there 
would  be  found,  in  many  cases,  a  net-work  of  dikes  of  lava 
ramifying  through  the  lower  interior  portion  of  the  cone,  and 
produced  in  a  way  which  has  already  been  indicated. 

Almost  all  the  older  authors  and  many  modern  ones  sup- 


Volcanoes.  57 

pose  that  all  volcanic  cones  have  been  built  up  in  this  simple 
manner.  The  theory  originated  by  Humboldt  and  elaborated 
by  Buch,  and  called  the  "  crater-of-elevation  theory,"  has 
found  many  warm  supporters  even  among  those  who  have 
worked  long  in  volcanic  regions,  while  it  has  been  persistently 
opposed  by  most  of  the  English  geologists,  especially  by  Lyell 
and  Scrope,  as  well  as  by  Dana  in  this  country.  According  to 
this  theory,  most  great  volcanoes  consist  of  two  portions,  very 
distinct  from  each  other  in  their  mode  of  formation.  The 
lower  part,  or  base  of  the  mountain  as  it  might  be  called,  con- 
sists of  strata  inclined  at  a  less  angle  than  the  upper,  and  has 
not  been  formed  by  the  accumulation  of  ejected  materials,  but 
consists,  rather,  of  stratified  masses,  which  may  have  been 
sedimentary  beds  deposited  horizontally,  or  volcanic  materials 
erupted  from  fissures  under  the  ocean.  In  either  case  these 
beds  are  supposed,  by  the  upholders  of  Buch's  theory,  to  have 
been  brought  into  their  present  inclined  position  by  a  "  bubble- 
shaped  elevation  of  the  ground,"  caused  by  pressure  of  the  vol- 
canic forces  confined  beneath.  On  this  inflated  mass,  through 
the  centre  of  which  the  lava  afterwards  found  its  way,  the  cone  of 
eruption  is  supposed  to  have  been  formed  in  the  ordinary  manner. 
In  many  cases,  however,  the  process  was  a  more  complicated 
one.  After  the  formation  of  the  flattened  dome-shaped  mass, 
the  volcanic  energy,  exerting  itself  at  the  base  of  the  chimney 
by  which  the  dome  was  penetrated,  would  fracture  it  in  all  di- 
rections, force  lava  into  these  fissures,  swell  out  the  mass,  and 
gradually  open  a  great  crater  at  the  summit,  around  the  edge 
of  which  the  strata  would  stand  at  a  much  greater  angle  than 
they  originally  had,  it  being  maintained  by  Buch  and  the  up- 
holders of  the  elevation  theory  that  lava  could  not  consolidate 
in  thick  beds  on  steep  slopes,  —  an  assertion  which  has  been 
abundantly  disproved  by  observations  in  different  parts  of  the 
world. 

It  is  in  this  condition  of  dome-shaped  elevation,  caused  by 
pressure  from  beneath,  that  Vesuvius  is  supposed  to  have  been 
at  the  time  Spartacus  camped  in  its  crater,  just  before  the 
great  eruption  of  79.  At  the  time  the  explosion  took  place, 
and  the  hidden  forces  obtained  an  outlet,  one  side  of  the  crater 
of  elevation  was  blown  off,  and  an  ordinary  ash  and  cinder 


58  Volcanoes. 

cone  began  to  form  in  the  cavity.  The  same  mode  of  formation 
is  claimed  for  Etna  by  Elie  de  Beaumont,  one  of  the  most 
zealous  supporters  of  Buch's  theory,  who  maintained  that 
the  lower  portion  of  this  great  volcano  was  quite  distinct  in 
its  formation  from  the  upper ;  that  the  one  was  formed 
beneath  the  sea  by  the  elevation  of  horizontally  deposited 
strata,  while  the  other,  or  the  cone  proper,  —  which  is  eleven 
hundred  feet  high  and  has  as  steep  an  angle  as  thirty-two  de- 
grees,—  was  built  up  by  subaerial  accretions  exclusively. 

Buch  applied  his  theory  to  the  Peak  of  Teneriffe,  of  which 
he  made  a  most  detailed  examination,  and  endeavored  to  ex- 
plain by  it  the  formation  of  the  great  semicircular  wall  which 
encloses  the  peak  itself  and  the  cone  of  Chahorra.  This  en- 
circling precipice  is,  in  places,  full  two  thousand  feet  high  and 
no  less  than  eight  miles  in  its  longest  diameter.  Buch  also 
visited  and  described  with  minuteness  the  beautiful  island  of 
Palma,  a  little  west  of  Teneriffe,  which  is  another  of  these 
great  truncated  cones,  with  a  huge  and  deep  cavity  in  the 
centre,  called  by  the  natives  a  caldera  (kettle),  from  three  to 
four  miles  in  diameter,  and  walled  in  by  a  precipice  varying 
from  fifteen  hundred  to  twenty-five  hundred  feet  in  vertical 
height.  This  boundary  wall  is  so  steep  and  unbroken  that 
there  is  only  one  place  where  a  descent  is  possible  even  on  foot. 

This  kind  of  structure  —  namely,  an  encircling  ring,  of  enor- 
mous dimensions  compared  with  those  of  ordinary  craters,  with 
a  cone  in  the  centre  —  is  quite  common,  and  is  especially 
well  seen  on  some  volcanic  islands,  where  the  internal  struc- 
ture is  revealed  by  breaches  made  by  the  sea  in  the  exte- 
rior wall.  The  interesting  island  of  Santorin,  in  the  Grecian 
Archipelago,  is  a  good  instance  of  this  kind  of  arrangement, 
the  volcanic  fires  here  having  been  active  of  late,  and  the 
region  one  which  has  furnished  material  for  a  considerable 
•  number  of  volumes,  as  already  mentioned.  The  island  of 
Nisyros  has  a  similar  structure,  the  nearly  circular  crater  be- 
ing three  miles  in  diameter  and  surrounded  by  a  rim  which 
rises  from  two  thousand  to  twenty-three  hundred  feet  above 
the  sea.  The  island  of  St.  Helena  is  described  by  Mr.  Dar- 
^  /  win  as  a  trachytic  volcano,  encircled  by  a  broken  ring  of 
•  basalt,  measuring  eight  miles  in  diameter  one  way  and  four  the 


Volcanoes.  59 

other ;  the  internal  cliff  faces  are  nearly  perpendicular,  ex- 
cept that  they  have  in  some  places  flat  projecting  shelves  or 
ledges  cut  around  them  in  parallel  curves.  Barren  Island,  in 
the  Bay  of  Bengal,  and  the  Mauritius,  are  other  excellent  ex- 
amples of  the  same  interesting  type  of  structure.  The  en- 
circling crater  ring  of  the  last-named  island  measures  no  less  j 
than  thirteen  miles  in  diameter. 

Lyell,  in  the  tenth  edition  of  his  "  Principles  of  Geology," 
published  two  years  since,  has  gone  pretty  thoroughly  into 
the  question  of  the  applicability  of  Buch's  theory  to  both  Vesu- 
vius and  Etna,  giving  the  results  of  his  own  repeated  and  re- 
cent  examinations  of  these  classic  volcanoes,  and  pointing  out 
that  many  important  facts  had  been  misapprehended  by  those 
geologists  who  had  endeavored  to  show  that  the  crater-of-ele- 
vation  theory  was  the  only  one  applicable  to  explain  their  form 
and  structure.  Hoffmann,  many  years  ago,  after  a  careful 
study  of  Vesuvius,  abandoned  the  theory  of  Buch,  which  he 
had  previously  maintained.  Of  eminent  French  geologists, 
Cordier  and  Constant  Prevost  were  also  opposed  to  the  idea 
of  the  building  up  of  volcanoes  in  any  other  way  than  by  the 
piling  of  one  layer  of  ejected  materials  upon  another. 

The  principal  difficulty  which  those  who  do  not  support  the 
crater-of-elevation  theory  have  to  meet  is  the  enormous  size  of 
some  of  these  great  encircling  rings,  which  would  seem  at  first 
too  large  to  be  the  result  of  explosive  forces,  implying  as  they 
do  an  astonishingly  violent  action  and  areas  of  vast  dimen- 
sions over  which  the  volumes  of  vapor  must  have  been  driven 
upwards. 

There  are  craters  of  gigantic  size,  however,  in  regard  to 
which  it  seems  clearly  demonstrated  that  they  were  formed  in 
the  ordinary  way,  that  is,  by  the  aggregation  of  materials 
erupted  from  a  central  orifice.  Thus  Kilauea  does  not  bear  any 
marks  of  being  a  crater  of  elevation  ;  neither  does  the  grand 
Haleakala,  on  the  island  of  Manui,  which  is  estimated  to 
be  some  thirty  miles  in  circumference.  Junghuhn,  who  has 
made  such  a  careful  examination  of  the  volcanoes  of  Java, 
gives  it  as  the  result  of  his  observations  that  the  great  cones  of 
that  island  have  all  been  formed  by  eruption,  and  not  by  eleva- 
tion ;  and  he  gives  most  excellent  reasons  for  drawing  this 


60  Volcanoes. 

inference,  —  Such  reasons,  indeed,  as  could  only  be  successfully 
opposed  by  proving  him  to  have  misstated  the  facts.  Similar 
conclusions  have  been  arrived  at  by  the  writer  of  this  article, 
after  examining  several  of  the  great  cones  on  the  Pacific  coast 
of  North  America. 

If  we  consider  what  prodigious  masses  of  material  are  thrown 
out,  as  already  mentioned,  in  such  eruptions  as  that  of  Tem- 
boro  or  Coseguina,  it  will  not  be  difficult  to  understand  that  a 
cavity  of  corresponding  size  must  be  left  behind ;  and,  as  a 
means  of  enlarging  such  a  cavity  to  an  almost  indefinite  ex- 
tent, we  may  call  in  both  subaerial  and  submarine  erosion, 
although  the  former  has  probably  been  usually  by  far  the  most 
effective  agent  in  this  respect.  That  any  such  great  blister-like 
uplift  of  the  superficial  crust  as  was  imagined  by  Humboldt  to 
account  for  the  dome-shaped  base  of  Jorullo  ever  occurred 
seems,  on  the  whole,  highly  improbable.  His  idea  of  a  hollow 
crust  or  roof  blown  up  over  a  vast  empty  space  beneath  will 
hardly  be  adopted  by  any  geologist  at  present.  Everything 
indicates,  on  the  contrary,  that,  instead  of  there  being  a 
vacuum  or  a  space  filled  only  with  gaseous  substances  under 
or  over  the  centre  of  the  volcanic  action,  there  is  much  more 
likely  to  be  a  crowding  together  in  that  region  of  fluid  ma- 
terial, seeking  to  find  a  vent.  That  great  areas  of  stratified 
deposits  might,  under  such  conditions,  be  elevated  into  dome- 
shaped  masses,  is  certainly  not  impossible  ;  and  yet  it  is  ques- 
tionable whether  the  fact  of  any  such  occurrence  has  ever  been 
demonstrated.. 

It  is  indeed  curious  that  the  great  name  of  Buch  —  a  man 
once  the  very  leader  of  geological  science,  and  to  whom  Hum- 
boldt dedicated  his  Kleiner e  Schriften  in  these  words  :  "  Dem 
geistreichen  Forscher  der  Natur,  dem  grossten  Geognosten  un- 
seres  Zeitalters,  Leopold  von  Buch  "  —  should  for  many  years 
back  have  been  most  frequently  quoted  in  order  to  bring 
forward  fresh  evidence  against  some  one  of  his  favorite 
theories,  or  to  show  how  thoroughly  he  misapprehended  some 
great  geological  phenomenon,  like  that  of  the  distribution  of 
the  glacial  boulders  in  Switzerland.  Still  the  fact,  however  dis- 
couraging it  may  seem  to  those  looking  simply  to  permanence 
of  personal  reputation,  is,  in  reality,  an  indication  of  progress 


Volcanoes.  61 

in  the  science.  Had  Buch  made  a  thorough  examination  of 
the  geologically  classic  region  of  Southern  Tyrol,  he  never 
would  have  given  to  the  world  a  theory  so  entirely  unsupported 
by  facts  as  that  by  which  he  sought  to  explain  the  formation  of 
the  wonderfully  picturesque  cliffs  of  dolomite  which  have  made 
that  country  so  celebrated,  and  the  origin  of  the  rock  of  which 
they  are  composed.  The  day  of  generalizations  of  a  magnitude 
entirely  disproportionate  to  the  slender  base  of  facts  on  which 
they  rest  has  passed  away ;  or,  at  least,  the  practice  of  bringing 
such  theories  forward  with  the  positiveness,  and  upholding 
them  with  the  obstinacy,  of  a  Buch,  is  one  which  is  no  longer 
in  vogue. 

There  are,  indeed,  many  geological  phenomena  the  theory  of 
which  is  obscure  and  difficult,  and  for  whose  final  elucidation  the 
stock  of  accumulated  observation  is  still  insufficient.  If,  with 
the  view  of  directing  attention  to  deficiencies  in  this  stock,  rath- 
er than  of  parading  his  actual  knowledge,  the  geologist  groups 
these  facts  together,  and  endeavors  to  show  in  what  direction 
they  seem  to  point  or  what  the  ultimate  solution  of  the  problem 
will  probably  be,  he  will,  if  his  work  be  done  in  the  right  spirit, 
not  incur  the  charge  of  rashly  generalizing  or  of  endeavoring 
to  force  his  opinions  on  others.  Among  the  obscurest  and  yet 
most  attractive  topics  of  geological  investigation  it  would  be 
safe  to  include  the  theory  of  volcanoes  and  earthquakes,  and 
especially  the  connection  of  their  phenomena  with  those  move- 
ments of  the  earth's  crust  which  have  resulted  in  the  forma- 
tion of  continents  and  mountain-chains,  and  which,  by  altering 
the  relative  level  of  land  and  sea,  have  played  the  principal 
part  in  the  long  series  of  events  that  have  been  going  on 
since  our  planet  became  the  theatre  of  geological  changes. 
This  article,  and  one  in  the  preceding  number,  may  be  con- 
sidered as  leading  the  reader  to  a  point  from  which  he  will  be 
able,  with  profit,  and,  it  is  to  be  hoped,  not  without  pleasure,  to 
survey  the  indicated  field,  .and  we  shall  endeavor  at  a  future 
time  to  act  as  his  guide  in  such  a  survey.  Before  closing,  we 
must  add  a  few  pages  to  what  has  been  said  in  a  previous 
article,  in  regard  to  the  geographical  distribution  of  volcanoes, 
or  their  arrangement  upon  the  earth's  surface. 

By  far  the  most  interesting  fact  in  this  connection  is  the 


62  Volcanoes. 

proximity  to  the  ocean  of  almost  all  active  volcanic  vents. 
Probably  nine  tenths  of  them  are  distributed  around  the 
Pacific,  forming  what  has  been  aptly  called  a  "  circle  'of 
fire "  full  twenty  thousand  miles  in  length.  The  islands 
on  the  west  side  of  that  ocean  form  almost  a  continuous 
chain,  beginning  with  the  Aleutians  on  the  north,  and  extend- 
ing to  New  Zealand  on  the  extreme  south.  This  is  pre-emi- 
nently a  region  of  active  volcanism,  for  hardly  a  single  one  of 
the  numerous  islands  in  the  various  groups  of  which  this  belt 
is  made  up  is  entirely  destitute  of  active  vents,  while  on  some  of 
them  they  are  crowded  together  by  the  hundred.  In  the  groups 
of  the  Formosa,  Philippine,  Molucca,  and  Sunda  Islands, 
there  is  perhaps  the  greatest  concentration  of  volcanic  energy 
which  our  planet  exhibits.  Nor  is  the  east  side  of  the  Pacific 
less  bountifully  supplied  with  indications  of  igneous  activ- 
ity. Along  the  whole  coast,  from  Patagonia  to  Alaska,  the 
eruptive  formations  are  displayed  on  the  grandest  possible 
scale,  although  the  regions  of  present  activity  are  sometimes 
widely  separated  from  each  other,  and  the  volcanic  belt,  taken 
as  a  whole,  presents  evidences  of  a  very  considerable  slacken- 
ing of  its  energy  since  the  close  of  the  Tertiary  period. 

In  the  South  American  Andes  the  active  volcanoes  are 
chiefly  limited  to  three  great  systems, — those  of  Chili,  Bolivia, 
and  Quito.  Each  of  these  has  its  grand  cones,  among  which 
are  the  highest  points  in  the  world,  with  the  exception  of  a 
few  in  the  Himalaya.  Aconcagua,  the  monarch  of  the  Chilian 
group,  lacking  not  much  of  twenty-three  thousand  feet  in 
-height,  has  been  generally  supposed  to  be  a  volcano,  and  was 
even  reported  by  Darwin  as  having  been  in  eruption  in  1835. 
Some  doubts  have  been  thrown  on  this  statement,  however,  by 
M.  Pissis,  a  topographical  engineer,  who  has  been  employed  for 
years  by  the  government  of  Chili  in  making  a  map  of  that 
country,  and  who  maintains  that  Aconcagua  consists  of  rocks 
of  the  Cretaceous  series.  It  is  curiously  indicative  of  the 
feebleness  of  the  spark  of  scientific  inquiry  which  is  kept  alive 
even  in  the  most  enlightened  of  all  the  South  American  states, 
that  so  interesting  a  question  should  not  have  been  definitely 
settled  a  long  time  ago.  Still  higher  than  Aconcagua  is 
Sahama,  chief  of  the  Bolivian  group,  and  only  surpassed  in 


Volcanoes.  63 

elevation,  on  the  American  continent,  by  Illimani  and  Illampu. 
It  is  twenty-four  thousand  feet  high,  or  one  thousand  feet 
higher  than  Chimborazo,  which  was  long  supposed  to  be  the 
most  elevated  mountain  mass  of  the  New  World,  but  which, 
although  the  loftiest  of  the  magnificent  group  which  sur- 
rounds the  plain  of  Quito,  is  only  21,420  feet  in  height. 
Off  the  coast  of  Central  and  South  America,  at  a  consid- 
erable distance,  however,  are  groups  of  volcanic  islands,  with 
long  intervals  between  them,  which  may  be  compared  with 
the  similar,  but  far  more  closely  crowded  ones  on  the  oppo- 
site side  of  the  Pacific.  Along  the  line  of  these  groups,  with- 
in the  intervals  between  them,  frequent  volcanic  submarine 
eruptions  have  been  observed,  which  have  given  rise  to  islands ; 
these,  however,  have  since  been  mostly  washed  away.  If 
we  may  judge  of  the  future  by  what  has  occurred  in  the  past, 
it  would  be  safe  to  predict  that,  as  volcanic  action  dies  out  on 
the  present  coast  line,  a  new  belt  will  be  gradually  added  to 
the  continent  on  the  west  side.  We  might,  without  being  con- 
sidered as  indulging  in  a  fanciful  speculation,  say  that  the  pro- 
cess of  adding  such  a  belt  on  the  Asiatic  side  was  already  far 
advanced,  while  on  the  American  it  is  just  beginning.  The 
most  remarkable  instance  of  insular  volcanism  on  the  east 
side  of  the  Pacific  is  the  group  of  the  Galapagos,  five  hundred 
miles  off  shore,  in  the  latitude  of  Quito.  This  group  consists 
of  five  principal  islands  and  several  smaller  ones,  all  vol- 
canic. Craters  have  been  seen  in  eruption  on  two  of  these, 
and  on  several  of  the  others  the  streams  of  lava  have  quite  a 
fresh  appearance.  The  number  of  craters  on  the  group  is  » 
very  great,  having  been  estimated  by  Darwin  at  as  high  a  : 
number  as  two  thousand. 

The  volcanic  phenomena  of  the  west  coast  of  North  America 
are  on  a  still  grander  scale  than  those  of  the  southern  half 
of  the  continent,  as  far  as  the  extent  of  the  area  covered  by 
igneous  products  is  concerned.  There  are  not,  however,  as 
many  very  lofty  cones,  and  not,  in  general,  as  much  present 
activity.  The  highest  development  of  volcanism  on  that  coast 
seems  to  have  occurred  just  at  the  close  of  the  Tertiary  epoch, 
and  at  that  time  the  activity  of  the  internal  forces  must  have 
been  prodigious.  In  spite  of  the  immense  erosion  which  has 


64  Volcanoes. 

taken  place  since  that  time,  the  proofs  of  this  activity  are  every- 
where visible  along  the  whole  line  of  the  coast  from  Central 
America  to  Alaska.  The  regions  of  active  volcanic  excitement 
on  the  Pacific  coast  of  our  continent  are  at  present  but  two  in 
number,  and  these  are  placed  at  the  two  extremities  of  the 
line,  one  in  Central  America  and  Southern  Mexico,  the  other  in 
Alaska  and  the  Aleutian  Islands.  The  southern  region  is 
divided  into  two  groups,  the  Central  American  and  the  Mex- 
ican ;  the  former  begins  with  the  volcano  of  Chiriqui  and  ex- 
tends to  that  of  Soconusco,  on  the  Isthmus  of  Tehuantepec,  — 
a  distance  of  full  eleven  hundred  miles.  This  group  is  re- 
markable, not  only  on  account  of  its  parallelism  with  and  close 
proximity  to  the  coast,  but  for  the  number  and  size  of  the 
cones  of  which  it  is  made  up ;  of  these  there  are  more  than 
fifty,  almost  all  on  the  summit  or  else  on  the  western  flank  of 
the  Cordilleras.  Perhaps,  with  the  exception  of  Java,  there 
is  no  region  in  the  world  where  the  volcanic  vents  are  so 
crowded  together.  Of  all  the  eruptions  which  have  taken  place 
here  during  the  historical  period,  that  of  Coseguina,  in  1835, 
already  mentioned,  was  the  most  astonishing.  The  ashes 
thrown  out  at  that  time  produced  darkness  for  two  days  over  a 
great  extent  of  country,  and  covered  an  area  as  large  as  that 
of  New  England  to  the  depth  of  several  feet,  the  noise  being 
heard  in  Jamaica  and  at  Bogota. 

Four  hundred  miles  north  of  Soconusco,  and  exactly  in  a 
line  with  the  prolonged  axis  of  the  Central  American  volcanic 
belt,  rises  the  cone  of  Popocatapetl,  generally  considered  the 
loftiest  point  of  North  America,  and  certainly  the  highest  which 
has  been  accurately  measured.  Its  only  possible  rival  is  its  near 
neighbor,  Orizaba,  which  has  been  made  by  some  late,  but  not 
very  trustworthy,  measurements  a  little  the  higher  of  the  two. 
Popocatapetl  has  been  repeatedly  measured  with  closely  coinci- 
dent results,  so  that  we  probably  know  its  height  within  twenty- 
five  feet ;  it  is  about  17,750  feet.  Both  these  great  cones  belong 
to  the  chain  of  lofty  volcanic  vents  which  traverses  the  conti- 
nent, in  the  direction  of  east  and  west,  nearly  in  the  latitude  of 
the  city  of  Mexico.  Beyond  this  belt  to  the  north,  within  the 
limits  of  Mexico,  there  are  no  active  volcanoes ;  nor  are  there 
any  on  the  peninsula  of  Lower  California,  as  is  uniformly 


Volcanoes.  65 

reported  in  all  the  books  ;  there  are  but  few  volcanic  cones 
even,  although  rocks  of  this  character  in  the  form  of  dikes 
and  sheets  of  lava  are  abundant  in  some  parts  of  the  peninsula. 
The  volcanic  formations  on  the  mainland  opposite  are  exten- 
sive and  wonderfully  varied  in  character;  but  they 'all  belong 
to  a  past  epoch  of  activity. 

Crossing  the  Mexican  boundary,  and  entering  our  own 
territory,  we  find  eruptive  rocks  abundant ;  and,  on  reaching 
the  parallel  of  35°,  a  little  to  the  north  of  the  centre  of 
Arizona,  another  great  volcanic  belt  may  be  traced  across 
the  Cordilleras,  in  a  line  transverse  to  their  general  trend. 
The  most  prominent  cones  of  this  belt  are  Mount  Taylor, 
San  Francisco  Mountain,  and  Bill  Williams's  Peak,  all  mag- 
nificent mountains,  probably  between  twelve  and  fourteen 
thousand  feet  high,  but  none  of  them  has  been  ascended  or 
accurately  measured.  They  rise  grandly  from  the  plateau  of 
horizontally  stratified  rocks,  and  are  surrounded  by  vast  lava 
fields  bearing  all  the  marks  of  having  been  erupted  at  no 
very  remote  period,  although  there  are  no  indications  of  pres- 
ent activity. 

Passing  up  through  California  and  Nevada,  we  find  all  along 
both  slopes  of  the  Sierra  Nevada,  and  on  the  parallel  ranges 
east,  entirely  through  to  Salt  Lake,  abundant  evidences  of 
former  volcanic  action,  on  the  grandest  possible  scale.  On  the 
east  side  of  the  mountains,  this  condition  of  activity  seems  to 
have  ceased  at  the  commencement  of  the  present  geological 
epoch,  or  at  least  to  have  diminished  greatly  in  violence.  The 
only  indications  of  present  volcanic  activity  along  the  Sierra 
Nevada,  south  of  the  north  line  of  California,  —  aside  from  the 
numerous  hot-springs,  —  are  some  comparatively  faint  remains  of 
solfataric  action  on  a  few  of  the  highest  points.  Thus  Lassen's 
Peak,  for  instance,  has  several  quite  large  areas  where  sulphur- 
ous gases  escape  from  pools  of  hot  water  and  boiling  mud, 
while  near  the  summit  of  Mount  Shasta,  amid  the  eternal  snow, 
there  is  a  hot-spring  from  which  sulphurous  vapors  are  con- 
stantly issuing.  Between  these  two  lofty  volcanoes,  one  nearly 
11,000  and  the  other  14,440  feet  high,  there  are  many  others, 
some  with  wonderfully  well-preserved  craters,  looking  as  if 
of  very  recent  formation,  yet  entirely  destitute  of  any  traces 
5 


66  Volcanoes. 

of  present  activity.  On  the  eastern  slope  of  the  Sierra,  near 
Mono  Lake,  are  a  number  of  lofty  and  beautifully  regular  cones 
with  well-defined  terminal  craters,  yet  apparently  quite  extinct. 
All  through  the  State  of  Nevada,  indeed,  the  mountain  ranges 
are  extensively  flanked  by  vast  accumulations  of  lava,  and 
when  we  cross  the  Humboldt  River,  and  traverse  the  region 
north  of  the  parallel  of  41°,  we  find  a  continuous  covering 
of  volcanic  materials  extending  over  all  the  northern  portion 
of  Nevada  and  California,  as  well  as  Southern  Idaho,  Eastern 
Oregon,  and  Washington  Territory.  This  region,  which  is  cov- 
ered almost  exclusively  with  basaltic  lava,  is  but  little,  if  any, 
less  than  six  hundred  miles  square,  and  occupies  an  area  con- 
siderably larger  than  France  and  Great  Britain  combined.  It 
is  by  erosion  of  rocks  of  this  character  that  the  many  beautiful 
waterfalls  of  the  Snake,  Pelouse,  and  other  rivers  have  been 
formed.  Those  of  the  Snake  River  are  described  by  the  few 
who  have  seen  them  as  of  surpassing  grandeur.  They  must 
be  among  the  very  finest  in  the  world,  taking  into  account 
height,  volume  of  water,  and  attractiveness  of  the  surrounding 
scenery. 

North  of  the  California  line  the  belt  of  nearly  extinct  vol- 
canic activity  is  continued  in  the  Cascade  Range,  —  the  prom- 
inent peaks  and  cones  of  that  chain,  which  is  in  fact  a  contin- 
uation of  the  Sierra  Nevada,  being  all  of  volcanic  origin.  The 
-  best  known  ones  south  of  the  Columbia  River  are  —  naming 
them  from  south  to  north  —  Mount  Pitt,  the  Diamond  Peaks, 
the  Three  Sisters,  Mount  Jefferson,  and  Mount  Hood.  The  latter 
is  a  magnificent  cone,  very  conspicuous  over  a  great  extent  of 
country,  and  much  looked  up  to  and  respected  by  the  Ore- 
gonians,  who  were  very  wroth  at  having  its  boasted  17,000  or 
18,000  feet  cut  down  by  the  ruthless  hand  of  science  to  11,225. 
North  of  the  Columbia  are  Mount  Adams  and  Mount  St.  Helens, 
which  are  in  nearly  the  same  parallel ;  then,  Mount  Rainier, 
standing  in  solitary  grandeur  about  seventy  miles  east-south- 
east of  Olympia ;  and  finally,  Mount  Baker,  near  the  line  of 
British  Columbia.  Of  these  great  cones,  Mount  Rainier  is 
the  noblest :  as  seen  from  Puget's  Sound,  covered  with  snow 
nearly  down  to  its  base  even  late  in  the  summer,  it  is  truly 
a  magnificent  object.  Its  summit  has  never  been  reached,  so 


Volcanoes.  67 

far  as  we  can  ascertain,  while  all  the  other  important  cones  of 
this  region  have  been  repeatedly  ascended.  That  any  of  these 
volcanoes  have  emitted  streams  of  lava  since  the  country  be- 
came known  to  the  whites  is  not  probable ;  but  that  ashes  have 
been  thrown  out  from  two  of  them,  Mount  St.  Helens  and 
Mount  Baker,  seems  to  be  well  authenticated.  The  newspapers 
have  frequent  accounts  of  columns  of  vapor  being  seen  to  issue 
from  Mount  Hood,  and  of  other  indications  of  activity  being 
displayed  by  the  great  cones  which  are  such  conspicuous  objects 
to  those  passing  up  and  down  the  Columbia.  These  stories, 
when  not  intentional  fabrications,  may  perhaps  be  attributed  to 
the  fact  that  sometimes  on  clear  days  the  moisture  in  the  air 
blowing  from  the  ocean  is  condensed  around  the  cool,  snow- 
covered  summits  of  the  cones,  so  as  to  have  somewhat  the 
appearance  to  a  not  very  critical  eye  of  clouds  of  vapor  issuing 
from  them.  We  obtained  pretty  satisfactory  testimony  that 
Mount  Hood  at  least  had  shown  no  signs  of  activity  during  the 
past  eight  or  ten  years. 

There  are  also  most  conflicting  statements  with  regard  to 
the  condition  of  the  volcanoes  through  British  Columbia  and 
Alaska.  Thus  Scrope,  a  careful  and  trustworthy  authority, 
says  of  Mount  St.  Elias,  that  it  has  certainly  been  seen  in 
eruption,  while  Grewingk,  a  well-known  geologist  who  ex- 
plored that  region  and  carefully  examined  all  the  published 
authorities  on  the  subject,  declares  that  none  of  these  volca- 
noes—  St.  Elias,  Edgecombe,  Fairweather,  etc.  —  have  been 
active  during  the  historical  period,  or,  at  least,  that  there  is  no 
evidence  of  any  such  activity. 


VOLCANISM  AND  MOUNTAIN-BUILDING. 


IN  two  articles  published  in  previous  numbers  of  this  Review 
(Yols.  CYIII.  page  578,  and  CIX.  page  231)  we  have  dis- 
cussed the  phenomena  of  earthquakes  and  volcanoes,  endeav- 
oring to  convey  in  popular  language  some  idea  of  the  nature, 
extent,  and  frequency  of  these  remarkable  manifestations  of 
the  internal  forces  of  the  earth.  In  the  last  of  these  two  arti- 
cles it  was  suggested  that  occasion  would  be  taken  to  continue 
the  consideration  of  the  subject,  and  to  endeavor  to  explain,  or 
at  least  throw  some  light  on,  the  nature  and  connection  of  the 
chief  causes  which  have  been  concerned  in  carrying  on  that 
complicated  series  of  geological  dynamics  which  we  include 
under  the  comprehensive  term  "  volcanism,"  and  of  which  the 
earthquake  and  volcano  are  two  of  the  most  striking  manifesta- 
tions. The  subject  is  one  which  has  always  commanded  the 
attention  of  geologists,  and  suggested,  or  even  provoked,  dis- 
cussion among  them.  The  difficulties  which  it  presents,  how- 
ever, become  apparent,  when  we  learn,  through  examina- 
tion of  the  printed  records  of  these  discussions,  how  little 
agreement  there  is  among  geological  authors,  and  how  widely 
they  differ  in  regard  to  points  which,  as  one  would  suppose, 
ought  long  since  to  have  been  settled. 

We  have  repeatedly,  in  the  course  of  the  preceding  articles, 
referred  to  the  intimate  relationship  existing  between  the  phe- 
nomena of  earthquakes  and  volcanoes,  —  a  relationship  which 
can  hardly  fail  to  have  become  apparent  to  all  who  have  given 
even  a  limited  amount  of  thought  to  the  subject.  We  have 
now,  however,  to  go  one  step  further  in  the  same  direction,  and 
show  how  the  consideration  of  the  subject  of  volcanism  leads 
most  directly  and  naturally  to  that  of  the  formation  of  moun- 
tain chains,  or,  in  still  more  general  language,  to  the  study  of 
6 


70  Volcanism  and  Mountain-Building. 

the  forces  which  have  drawn  the  outlines  of  the  continents  and 
moulded  the  surface  of  the  earth  into  its  present  relief. 

The  difference  of  elevation  between  the  summit  of  the  high- 
est land  and  the  bottom  of  the  deepest  ocean  is  but  trifling,  as 
compared  with  the  whole  diameter  of  the  globe,  yet  of  what 
immense  importance  in  the  economy  of  nature  are  our  moun- 
tain chains,  and  how  thoroughly  are  our  most  weighty  interests 
and  avocations  dependent  on  the  form  and  elevation  of  the 
continental  masses !  Mountains  as  geographical  and  geo- 
logical facts  are  of  the  highest  significance  to  the  student  of 
natural  phenomena,  in  whatever  light  he  considers  them.  As 
agents  in  determining  the  character  of  the  climate,  the  courses 
of  rivers,  the  nature  of  the  soil,  the  migrations  of  nations,  the 
distribution  of  languages,  manners,  and  customs ;  in  short,  in 
their  relations  to  man  and  nature,  from  the  point  of  view  of 
physical  geography,  they  play  the  leading  part.  As  permanent 
records  of  past  geological  changes  in  the  history  of  the  earth, 
mountains  are  all  important  to  the  student  of  geology.  What 
would  this  branch  of  science  be,  without  mountains  and  the 
study  of  mountains  !  The  results  of  the  dynamics  of  the  globe 
are  registered  in  the  mighty  ridges  which  encircle  it,  and  mark 
the  outlines  of  its  continents  and  oceans.  Indeed,  we  can 
hardly  conceive  of  the  present  order  of  things  as  existing  at 
all  without  these  visible  results  of  the  manifold  causes  which 
have  worked  together  to  make  the  earth  habitable. 

Hence,  the  study  of  the  structure  and  mode  of  formation  of 
mountains  is  the  study  of  the  greatest  problems  with  which  the 
science  of  geology  presents  us.  Thoroughly  to  work  out  and 
comprehend  the  structure  of  all  the  mountain  chains  of  the 
world  would  be  little  different  from  thoroughly  working  out 
and  comprehending  its  geology.  There  is  hardly  a  problem 
presented  by  the  science  which  would  not  find  its  application 
in  some  one  of  our  mountain  systems.  Orography,  then,  or 
the  study  of  the  structure  of  mountain  chains,  is  the  study  of 
geological  phenomena  on  the  largest  scale  and  from  the  most 
generalized  point  of  view. 

It  cannot  fail  to  have  been  impressed  on  the  mind  of  the 
reader  of  the  preceding  articles,  that  there  is  an  intimate  con- 
nection, in  the  character  of  the  results  at  least,  between  the 


Vblcanism  and  Mountain-Building..  71 

forces  by  which  volcanic  and  earthquake  action  is  kept  up  and 
mountains  originated.  A  volcano  is,  in  fact,  a  mountain,  and 
to  the  popular  mind  there  is  little  difference  between  an  isolated 
elevation  and  a  group  or  line  of  them ;  between  a  mountain 
and  a  chain  of  mountains,  in  short.  But  not  a  few  of  the  latter 
are  almost  or  quite  exclusively  aggregations  of  volcanic  mate- 
rial ;  and  when  we  come  to  rocks  which  are  eruptive,  that  is, 
which  have  been  poured  forth  from  the  interior  of  the  earth, 
although  not  technically  volcanic,  we  find  that  these  constitute 
a  large  portion  of  a  great  many  mountain  chains,  and  especially 
of  the  highest  and  grandest.  And  the  more  we  look  into  the 
matter  the  more  we  shall  be  convinced  that  the  formation  of 
mountains  and  the  development  of  continents  are  also  closely 
correlated  phenomena.  Mountains  are  but  the  skeletons  of  the 
continents.  Wherever  a  lofty  chain  of  mountains  has  been 
raised  above  the  sea-level,  there  is  a  central  mass  with  a  ten- 
dency to  grow  and  spread  itself  laterally,  under  the  influence 
of  denuding  agencies ;  and,  unless  counteracted  by  a  general 
subsidence,  there  will  be  a  steady  increase  of  breadth  of  the 
region,  at  the  expense  of  the  height  of  the  more  elevated  por- 
tion. If  the  material  is  carried  down  and  deposited  under  the 
ocean,  then,  whenever  there  is  a  change  in  the  relative  level 
of  sea  and  land,  so  as  to  bring  the  newly  formed  strata  above 
the  water,  these  will  be  found  to  present  evidences  of  the  con- 
ditions under  which  they  were  deposited,  in  the  form  of  marine 
fossils,  which  will  be  more  or  less  abundant,  according  as 
the  physical  conditions  varied  at  the  time  the  deposition  took 
place.  If  two  chains  of  mountains  are  so  situated  with  re- 
spect to  each  other  that  continental  growth  may  take  place  be- 
tween them,  the  process  will,  of  course,  be  the  more  rapid,  and 
the  newly  made  land  will  cover  a  proportionably  greater  area. 
Every  continental  mass,  then,  will  be  found  on  analysis  to  con- 
sist of  one  or  more  chains  or  groups  of  mountains,  and  large 
areas  of  lower  land  which  has  been  derived  from  the  long-con- 
tinued erosion  of  the  more  elevated  regions.  An  examination 
of  good  topographical  maps  of  the  different  continents  will 
show  this  relation  most  clearly  ;  especially  if  aided  by  sections 
across  the  land-masses  transverse  to  the  direction  of  the  leading 
chains  of  mountains  which  traverse  them. 


72  Volcanism  and  Mountain-Building. 

It  is  clear,  then,  that  when  looking  at  the  subject  from  the 
broadest  point  of  view,  and  endeavoring  to  make  out  what 
agents  of  geological  change  have  been  most  widespread  and 
general  in  their  action,  we  cannot  separate  the  phenomena  of 
volcanoes  and  earthquakes  from  those  of  mountain-building 
and  continental  growth.  One  key  must  give  access  to  all  the 
mysteries  of  geological  dynamics.  The  nature  of  this  key  was 
first  rather  vaguely  shadowed  forth  by  Leibnitz  in  his  "  Pro- 
togaea  "  ;  but  the  key  itself  was  not  really  forged  until  long  after, 
when  Humboldt  began  to  group  the  physical  phenomena  of  the 
universe  into  one  harmonious  picture,  or  cosmos.  Leibnitz  rec- 
ognized the  fact  that  the  earth  had  cooled  from  a  condition  of 
igneous  fusion,  and  that  in  this  cooling  inequalities  of  the  sur- 
face would  be  likely  to  have  arisen.  But  it  was  reserved  for 
Humboldt  to  announce  a  cause  of  volcanic  action  which  would 
be  always  operative,  both  through  the  past  geological  ages 
and  in  all  future  time.  As  first  enunciated  by  him,  half  a  cen- 
tury ago,  it  was  intended  to  be  applied  solely  to  volcanic  phe- 
nomena, and  was  thus  expressed :  "  All  volcanic  phenomena 
are  probably  the  result  of  a  communication,  either  permanent 
or  transient,  between  the  interior  and  exterior  of  the  globe." 
Ten  years  later,  the  idea  of  one  general  cause  for  all  the  varied 
forms  of  volcanism  has  clearly  worked  itself  out  in  Humboldt' s 
mind,  and  was  thus  formulated  in  the  "  Kosmos  " :  "In  one 
comprehensive  view  of  nature,  these  all  (namely,  the  phenom- 
ena of  volcanism)  fuse  together  into  the  single  idea  of  the  reac- 
tion of  the  interior  of  our  planet  against  its  crust  and  surface." 

While  now  most  geologists  admit  the  validity  of  this  expla- 
nation, so  far  as  it  goes,  the  discrepancies  of  opinion  which 
have  arisen  in  showing  how  the  reaction  in  question  is  brought 
about  are  very  considerable.  As  long  as  the  theory  was  only 
vaguely  shadowed  forth,  and  no  attempt  was  made  to  go  into 
details,  but  little  objection  could  be  offered  to  it.  But  when,  as 
facts  began  to  accumulate  and  more  precision  of  statement  and 
clearness  of  development  were  required,  in  harmony  with  the 
progress  of  modern  thought,  the  difficulties  of  the  case  became 
more  and  more  apparent  and  the  divergencies  of  opinion 
greater.  Humboldt  may  be  said  to  have  furnished  a  blank 
key,  which  looked,  at  first,  as  if  it  would  fit  the  lock ;  but 


Volcanism  and  Mountain-Building.  73 

every  examination  lias  revealed  some  new  ward  to  which  it 
must  be  adapted;  and  different  observers  have  shown  them- 
selves very  much  in  doubt  as  to  how  it  was  to  be  filed  to  fit 
the  complications  which  they  had  discovered,  and  which  com- 
bine to  make  the  opening  of  the  lock  anything  but  the  simple 
task  which  it  seemed  at  first  to  be. 

As  time  passed  on,  and  the  various  borings  and  mining  oper-^ 
ations  all  over  the  world  gradually  gave  absolute  certainty  to 
the  at  first  rather  hesitatingly  received  fact  of  a  universal 
increase  of  temperature  in  descending  beneath  the  earth's 
surface,  the  views  of  Humboldt  began  to  be  generally  re- 
ceived and  acquired  something  like  this  form  :  The  earth  is 
gradually  cooling  from  a  condition  of  intense  heat  and 
igneous  fusion.  During  this  cooling  an  exterior  crust  or 
shell  has  been  formed.  This  crust  has,  from  time  to  time, 
been  endeavoring  to  adapt  itself  to  the  still  shrinking  nucleus, 
and,  while  so  doing,  has  from  time  to  time  yielded  to  the  accu- 
mulating tension.  The  vibration  resulting  from  this  sudden 
yielding  has  been  the  principal  cause  of  earthquake  shocks, 
and  through  the  fissures  thus  formed  the  molten  matter  of  the 
interior  of  the  earth  has,  at  various  intervals,  found  its  way  to 
the  surface  in  the  form  of  volcanic  eruptions  and  accompanied 
by  all  the  phenomena  of  volcanic  action.  The  crust  of  the 
earth,  in  endeavoring  to  adapt  itself  to  the  nucleus,  has  been 
in  places  more  or  less  uplifted  or  depressed,  folded  or  plicated, 
thus  giving  rise  to  those  irregularities  of  the  surface  which  we 
call  mountains,  and  which,  also,  often  owe  their  existence  to  a 
direct  pouring  out  of  the  eruptive  material  through  an  elon- 
gated fissure,  this  material  then  forming  the  axis  of  the  moun- 
tain mass  or  range. 

Those  who  are  familiar  with  the  various  geological  text- 
books in  use  will  recognize  that  this  is  the  simplest  way  of 
expressing  the  generally  adopted  theory  ;  but,  as  will  presently 
be  seen,  there  is  the  widest  variety  of  opinions  and  hypotheses 
when  anything  like  an  approach  to  a  detailed  statement  of  the 
modus  operandi  of  the  internal  forces  is  attempted. 

In  the  first  place,  there  is  considerable  diversity  of  opinion 
among  geologists  as  to  the  manner  in  which  the  earth  has  con- 
solidated while  cooling.  "We  know  that  the  specific  gravity  of 


74  Volcanism  and  MountairtrBuilding . 

our  planet,  as  a  whole,  is  about  double  that  of  its  external 
crust ;  and  to  account  for  this  superior  density  of  the  interior, 
we  have  to  endeavor  to  combine  three  conditions,  in  regard  to 
each  of  which  there  is  much  uncertainty  ;  these  are,  the  nature 
of  the  materials  of  which  the  portion  of  the  earth  beneath  the 
crust  is  made  up,  the  amount  of  condensation  effected  on  this 
by  pressure  of  the  superincumbent  mass,  and  the  reaction  of 
the  internal  heat  against  that  pressure.  Of  course  if  the  in- 
terior of  our  planet  consisted  chiefly  of  metallic  iron,  or  any 
other  heavy  metal,  it  would  have  a  higher  specific  gravity  than 
if  silica  predominated ;  but,  even  if  exclusively  formed  of  a 
material  as  light  as  quartz,  the  earth  ought,  according  to  phys- 
ical laws,  to  be  even  much  denser  than  it  now  is,  unless  there 
be  some  cause  acting  to  diminish  the  condensing  effect  of  press- 
ure. Different  physicists  have  made  various  calculations  on 
this  subject,  the  results  of  which  are  not  very  satisfactory  in 
their  agreement  with  each  other.  But  it  is  certain  that  if  sub- 
stances continue  to  have  their  density  increased  by  pressure  in 
descending  towards  the  earth's  centre,  in  the  same  ratio  as  they 
are  found  to  do  at  the  surface  by  actual  experiment,  then  we 
should  have  to  penetrate  to  but  a  few  hundred  miles  in  depth,  to 
'  L  j  find  water  as  dense  as  platina,  and  all  other  substances  similarly 
;  compressed.  The  force  which  acts  against  compression,  so  as 
to  make  the  earth's  density,  as  a  whole,  only  twice  that  of  its 
crust,  is,  in  all  probability,  the  expansive  action  of  the  internal 
heat.  But  we  know  too  little  of  the  properties  of  bodies  at 
prodigiously  high  temperatures  and  under  immense  pressure, 
to  say  positively  whether,  under  such  circumstances,  the  mate- 
rials of  which  the  earth  is  made  would  have  a  solid  or  a  liquid 
form ;  and  neither  astronomy  nor  mathematics  have  been  able  to 
give  the  geologist  any  valuable  assistance  in  deciding  this  ques- 
tion. On  the  contrary,  the  most  eminent  authorities  in  these 
departments  of  science  have  published  the  most  contradictory 
statements  as  the  results  of  their  investigations  in  regard  to 
the  condition  of  the  interior  of  our  planet.  Hence,  so  far  as 
the  astronomical  evidence  goes,  geologists  are  at  liberty  to 
form  their  own  theories  on  this  subject,  and  some  have  inclined 
to  the  belief  that  the  earth  is  solid  throughout ;  others  stoutly 
maintain  that  it  consists  of  a  solid  nucleus,  with  a  liquid  shell 


Volcanism  and  Mountain-Building.  75 

near  the  exterior  crust ;  while  the  prevailing  opinion  has  been 
that  the  solid  crust  encloses  a  mass  of  matter  fluid  nearly  or 
quite  to  the  centre.  This  latter  idea  has  been  naturally  adopt- 
ed, because  we  are  accustomed  to  see  masses  of  melted  metal 
or  stone  cool  first  on  the  surface,  while  the  interior,  if  the 
mass  be  large,  remains  for  a  long  time  in  a  fluid  condition. 
The  theory  of  a  fluid  interior  has  also  been  sustained  by  con- 
siderations connected  with  the  widespread  distribution  of  vol- 
canic orifices,  and  the  vast  amount  of  liquid  matter  which  has 
been  poured  forth  from  them  at  different  epochs.  The  con- 
nection of  earthquake  shocks  with  the  phases  of  the  moon, 
adverted  to  in  a  previous  article,  is  not  without  an  important 
bearing  on  this  question.  The  results  attained  by  all  seismo- 
logists who  have  investigated  these  subjects  do  appear  to  indi-. 
cate  that  there  is  a  decided  action  of  the  moon  on  the  interior, 
analogous  to  that  which  it  exerts  on  the  waters  of  the  ocean. 
The  evidence  is  not  as  decisive  as  might  be  wished,  but  is  too 
important  to  be  overlooked  in  the  discussion  of  a  subject  where 
precise  data  are  hardly  to  be  obtained  or  expected.  The  later 
researches  in  physics,  however,  have  shown  that  there  is  no  such 
sharp  line  dividing  solids  from  liquids  as  was  formerly  supposed 
to  exist ;  and  all  the  requirements  of  geology  would  be  satisfied 
if  it  should  be  admitted  that  the  material  constituting  the  in- 
terior of  the  earth,  if  not  already  in  a  liquid  condition,  was 
capable  of  assuming  it  when  relieved  of  pressure  ta  a  certain 
extent. 

All  geologists  will  agree  in  this,  that  the  disturbances  of  the 
earth's  crust,  by  whatever  name  we  please  to  call  them,  when- 
ever acting  independently  of  attraction,  or  against  gravity,  are 
due  to  internal  heat.  This,  in  some  way  or  other,  is  the  cause 
of  all  earthquake  and  volcanic  action  as  well  as  of  mountain- 
building.  If  the  earth  were,  as  the  moon  appears  to  be,  en- 
tirely cooled  down,  the  heat  of  the  sun  and  the  attraction  of 
the  sun  and  moon  would  then  be  the  sole  dynamic  agents  in 
producing  geological  changes.  These  changes  would  be  af- 
fected chiefly  through  the  action  of  water.  The  tidal  current, 
raised  by  the  lunar  and  solar  attraction,  the  powerful,  although 
slowly  acting  agencies  of  rain  and  rivers,  —  these  would  be  the 
principal  agents  of  geological  change.  But  these  tend  almost 


76  Volcanism  and  Mountain-Building. 

exclusively  to  abrade  material  from  the  more  elevated,  and 
spread  it  out  again  upon  the  lower  regions.  Hence,  the  dy- 
namical agencies  at  work  on  the  earth's  surface,  supposing  the 
effects  of  internal  heat  to  be  no  longer  in  action,  would  be 
directed  to  reducing  inequalities  of  height ;  in  short,  to  level- 
ling down  the  mountains  and  filling  up  the  valleys.  The  char- 
acter of  the  changes  produced  by  the  internal  heat  of  the  earth, 
on  the  other  hand,  is  antagonistic  to  this ;  not  exclusively,  but 
nearly  so.  The  proof  of  this  is  visible  everywhere :  in  the 
mountain  ranges  and  single  peaks  made  of  lava  and  volcanic 
debris ;  in  the  ranges  having  an  axis  of  eruptive  rock,  which 
has  been  thrust  up  from  below  and  carried  the  overlying  strati- 
fied rocks  with  it ;  and  in  many  other  ways. 

It  being  universally  admitted  that  it  is  the  internal  heat  of 
the  earth  which  gives  rise  to  the  phenomena  of  volcanism,  we 
have  to  inquire  in  what  way  the  results  indicated  in  our  previ- 
ous articles  are  brought  about.  The  disturbances  of  the  crust 
by  earthquake  shocks  present  the  least  difficulty  in  their  expla- 
nation. Admitting  the  gradual  cooling  of  the  earth  as  a  whole, 
we  find  no  difficulty  in  understanding  that  this  cooling  may  be 
unequal  and  irregular  in  its  progress  and  distribution.  This 
unequal  cooling  cannot  fail  to  give  rise  to  unequal  tension  be- 
tween different  parts  of  the  crust ;  and  as  the  force  accumulates 
until  it  overcomes  the  resistance,  so,  from  time  to  time,  as  the 
yielding  takes  place,  there  will  be  a  sudden  jar  or  shock  given 
to  the  surrounding  region,  which  will  be  more  or  less  severe, 
according  to  the  amount  of  force  expended  in  overcoming  the 
resistance.  This  sort  of  operation  will  go  on  whether  the  ma- 
terials of  the  earth's  crust  expand  or  contract  on  cooling,  or 
even  if  they,  during  a  portion  of  the  cooling,  contract  and 
afterwards  expand.  That  this  is  the  origin  of  the  great  earth- 
quakes is  proved  conclusively  by  their  character  and  distribu- 
tion on  the  earth's  surface.  Their  association  with  coast  lines, 
mountain  chains  in  process  of  upheaval,  and  recent  geological 
formations,  affords  sufficient  evidence  that  they  are  not  local 
phenomena,  but  linked  in  the  closest  manner  with  those  other 
occurrences  which  have  to  do  with  the  building  up  of  moun- 
tains and  the  shaping  of  the  outlines  of  the  continents. 

Volcanic  phenomena,  on  the  other  hand,  are  vastly  more 


Vblcanism  and  Mountain-Building.  77 

difficult  to  decipher  and  refer  to  their  origin,  since  they  are 
more  complicated  in  every  respect,  involving  chemical  as  well 
as  mechanical  causes  and  results.  To  account  for  all  that  we 
know  of  volcanic  rocks  is  plainly  enough  a  difficult  task,  since 
hardly  any  two  eminent  authors  fully  agree  in  their  ideas  on 
this  subject.  And  the  larger  one's  experience  and  field  of 
observation  has  been,  the  more  difficult  the  task  of  reconciling 
and  correlating  all  the  phenomena  has  been  found  to  be.  Hence, 
the  theories  have  mostly  come  from  those  geologists  whose] 
training  has  been  chiefly  chemical,  and  who  have  looked  at  j  ^ 
nature  almost  exclusively  through  the  bars  of  their  laboratory  •* 
windows.  Those  whose  powers  of  observation  have  had  the 
widest  field  for  their  exercise  have  had  the  most  vivid  percep- 
tion of  the  complicated  character  of  the  phenomena  of  volcanic 
action,  and  have  usually  preferred  to  leave  their  correlation  to 
others. 

The  work  of  Bichthofen,  the  title  of  which  was  among  those 
placed  at  the  head  of  a  preceding  article  on  volcanoes,  forms 
an  exception  to  the  above  remarks,  since  its  author  has  had  an 
uncommon,  in  fact  almost  an  unparalleled,  range  of  observa- 
tion. Having  begun  with  the  critical  study  of  the  classic  vol- 
canic regions  of  Hungary  and  Transylvania,  he  was  enabled  to 
carry  his  researches  in  an  almost  unbroken. line  entirely  around 
the  globe,  ending  with  the  grandest  field  anywhere  presented 
to  the  geologist  in  this  department,  the  Cordilleras  of  North/  VV 
America.  In  several  respects  this  work  of  Richthofen's, — 
"  The  Natural  System  of  the  Volcanic  Rocks,"  as  it  is  called, — 
is  one  of  the  greatest  importance  to  the  student  of  dynamical 
and  structural  geology.  It  is  the  first  attempt  to  go  into  any- 
thing like  detail  in  the  investigation  of  some  of  the  most  diffi- 
cult problems  of  this  branch  of  the  science.  That  such  a  work 
should  not  meet  with  immediate  attention  on  the  part  of  the 
general  public  was  to  be  expected ;  that  it  should  undergo 
criticism  was  to  be  desired,  by  its  author,  no  doubt,  as  well  as 
others  ;  but,  that  its  positive  statements  of  facts  of  the  highest 
importance  in  their  bearing  on  the  phenomena  of  volcanism 
should  be  overlooked,  and  even  denied,  is  something  which  does 
not  argue  well  for  the  comprehensiveness  or  candor  of  those 
thus  placing  themselves  in  opposition  to  the  introduction  of  a 


78  Vblcanism  and  Mountain- Building. 

"  natural  system  "  into  that  which  before  had  no  system  at  all 
connected  with  it.  In  the  course  of  this  article  we  shall  en- 
deavor to  bring  out  some  of  the  more  prominent  features  of 
Richthofen's  great  paper,  and  will,  in  the  proper  place,  give 
an  idea  of  some  of  the  criticisms  which  have  been  made  upon 
it.  But  further  light  must  be  thrown  on  the  general  subject 
of  volcanism,  before  details  can  be  made  intelligible  to  the 
general  reader. 

If  we  had  only  the  volcanic  phenomena  of  the  present  day, 
or  active  volcanoes,  to  deal  with,  the  task  of  unravelling  their 
mysteries  would,  perhaps,  not  be  one  of  so  great  difficulty ; 
but,  as  soon  as  we  begin  to  elaborate  our  materials,  and  en- 
deavor to  correlate  the  results  obtained  in  the  various  lines  of 
research,  we  find  ourselves  confronted  by  an  immense  mass  of 
facts  going  to  show  that  our  present  volcanic  outbursts  are  only 
the  last  remains,  or  dying  out,  of  a  series  of  geological  events, 
the  scale  of  which  was  formerly  much  grander  than  it  now  is. 
We  find,  without  going  back  to  any  great  distance  in  geological 
history,  that  there  was  a  time  when,  instead  of  being  poured 
forth  from  scattered  isolated  orifices,  the  eruptive  material 
.  found  its  way  to  the  surface  through  linear  rents,  or  fissures, 
<  (  which  often  must  have  extended  for  hundreds,  or,  perhaps, 
even  thousands  of  miles.  We  find  the  material  which  has  thus 
been  poured  forth  occupying  the  surface  in  vast  sheets,  often 
lying  in  nearly  horizontal  beds,  and  covering  an  area  of  many 
thousand  square  miles.  We  find  vast  chains  of  mountains  al- 
most wholly  built  up  of  volcanic  rock,  and  we  are  able,  on  careful 
examination,  to  recognize  the  fact  that  these  masses  have  not 
been  brought  to  the  surface  in  lines  radiating  from  a  centre, 
that  centre  being  what  we  call  a  volcano ;  but  along  a  linear 
axis,  in  the  form  of  "  massive  eruptions,"  as  they  are  called  by 
Eichthofen,  who  has  been  the  first  person  to  clearly  distinguish 
between  the  two  kinds  of  eruptive  action,  and  to  give  a  name 
to  massive,  as  distinguished  from  ordinary  volcanic,  eruptions. 
The  necessity  of  keeping  in  mind  the  difference  between  vol- 
canic materials  erupted  from  a  crateriform  opening  and  those 
poured  forth  from  a  linear  fissure  was  made  evident  by  Pro- 
fessor Dana  more  than  twenty  years  ago,  in  his  admirable  gen- 
eralizations on  the  geological  results  of  the  earth's  contrac- 


Volcanism  and  Mountain-Building.  79 

tion  and  the  formation  of  continents.*  This  idea  was  also 
clearly  present  in  the  mind  of  Humboldt  at  the  time  of  the 
publication  of  the  first  volume  of  his  Kosmos,  and  Richthofen 
has  in  fact  carried  out  some  of  the  suggestions  then  made  by 
him  with  regard  to  the  necessity  of  investigation,  by  compe- 
tent lithologists,  of  the  different  portions  of  volcanic  ranges 
which  have  been  piled  upon  each  other  at  successive  epochs 
and  in  various  ways.  And  yet  we  find  Mr.  Scrope,  the  veteran 
author  of  a  much-quoted  general  work  on  volcanoes  and  of  the 
classic  description  of  Central  France,  denouncing  in  the  most 
violent  language  those  geologists  who  think  they  see  any  differ- 
ence in  the  manner  in  which  volcanic  rocks  are  now  and  have 
formerly  been  erupted. f  This  fact  alone  will  answer  as  a 
sufficient  demonstration  of  the  difficulties  which  the  study  of 
volcanic  rocks  presents,  and  of  the  disagreement  in  theoret- 
ical views  among  geologists,  as  soon  as  they  begin  to  enter  into 
details  with  regard  to  the  mode  of  volcanic  action.  J 

The  distinction  between  massive  and  volcanic  eruptions 
has  been  excellently  illustrated  by  Richthofen,  as  follows:  "It 
is  well  known  that  small  cones  are  frequently  met  with  on  the 
slopes  of  larger  volcanoes.  If  they  occur  in  large  number,  as 
on  Mount  Etna,  they  are  usually  situated  in  lines  which  radiate 
from  the  crater.  <  Each  of  them  is  built  up  of  layers  of  scoria 
and  ashes  sloping  away  from  the  centre,  where  a  crater  is  im- 
mersed, and  such  cones  will  occasionally  emit  currents  of  lava, 
and  be  in  fact  the  repetition  on  a  small  scale  of  the  mother 
volcano.  Just  as  these  parasitic  volcanoes  have  their  roots  in 
the  glowing  lava,  volcanoes  in  general  must,  as  is  demonstrated 

*  See  "  Geology  of  the  Exploring  Expedition,"  and  a  review  of  the  same  in  the 
North  American  Review,  Vol.  LXXIV.  p.  301,  by  the  author  of  this  article;  also 
American  Journal  of  Science  (2)  ii.  335  ;  iii.  94,  176,  381  ;  iv.  88;  vii.  379. 

t  See  Scrope  in  Geological  Magazine,  Vol.  VI.  p.  512.  ; 

J  Mr.  Scrope  goes  still  further  in  his  misconception  and  misrepresentation  of 
Richthofen's  views.  He  says,  "  the  value  of  M.  Richthofen's  "  —  to  an  English- 
man all  foreigners,  whether  German  barons  or  otherwise,  are  "M.s" — "Natural 
System  of  Volcanic  Rocks,  as  a  contribution  to  the  science  of  geology,  may  be  esti- 
mated from  the  fact  that  he  denies  the  occurrence  of  any  volcanic  rocks  in  the  series 
of  geological  formations  preceding  the  tertiary  era."  The  simple  fact  being  that 
"  M.  Richthofen  "  has,  for  convenience,  and  following  the  large  majority  of  authors, 
chosen  to  designate  the  eruptive  rocks  of  the  tertiary  era  as  "  volcanic,"  and  those 
of  preceding  epochs  in  another  manner. 


; 


80  Volcanism  and  Mountain-Building. 

by  their  mode  of  occurrence,  be  considered  as  parasites  on  cer- 
tain subterranean  portions  of  the  material  of  massive  eruptions, 
which  still  possess  a  high  temperature  and  are  kept  in  a  liquid 
state  by  the  molecular  combination  with  water  which  finds 
access  to  them." 

Richthofen  then  goes  on  to  show  that  this  mode  of  origin  of 
volcanoes  is  only  a  repetition  on  a  smaller  scale  of  the  manner 
in  which  massive  eruptions  themselves  originated.  Volcanoes 
bear  the  same  relation  to  massive  eruptions  which  the  latter 
do  to  the  material  forming  the  primeval  interior  of  the  globe. 
"What  is  this  material,  and  what  its  relation  to  the  rocks  which 
we  call  volcanic  ?  These  are  questions  which  we  have  to  en- 
deavor to  answer. 

We  must  first  try  to  ascertain  what  volcanic  rocks  really  are. 
All  are  familiar  with  the  distinction  between  igneous  and  sedi- 
mentary rocks,  that  is,  between  rocks  which  have  once  been  in 
a  molten  state  and  which  have  come  to  the  surface  or  been 
deposited  through  the  action  of  igneous  causes,  and  those  which 
have  been  deposited  by  water.  Most  persons  also  understand 
the  term  "  metamorphic  "  as  used  by  geologists,  meaning  that 
the  rocks  embraced  under  that  term  are  not  what  they 
once  were  ;  that  they  have  suffered  certain  chemical  changes 
since  their  deposition,  in  the  course  of  which  the  mass  has 
undergone  a  rearrangement  of  its  particles,  so  as  to  have  as- 
sumed a  crystalline  texture,  separate  and  distinct  minerals 
segregating  out  of  what  was  before  an  amorphous  mass  in 
which  no  particular  crystallized  minerals  could  be  discerned. 
Hence,  the  metamorphic  rocks  are  often  called  the  crystalline 
rocks.  This  distinction  of  rocks  into  igneous,  sedimentary,  and 
metamorphic  is,  of  course,  more  or  less  arbitrary.  For  instance, 
showers  of  pumice-stone  and  ashes  may  be,  and  often  have  been, 
thrown  from  a  volcano,  and  the  eruptive  material  falling  into 
water  will  then  have  assumed  a  stratified  condition  as  it  sank 
to  the  bottom,  just  as  any  mud  or  sand  would  do.  The  strata 
thus  formed,  having  been  raised  above  the  water,  or  while  still 
beneath  it,  may  have  undergone  chemical  changes,  or  become 
metamorphic  in  character,  so  that  the  mass  now  partakes  of 
the  character  of  all  three  classes. 

The  formation  of  sedimentary  rocks  implies  evidently  the 


Volcanism  and  Mountain-Building.  81 

pre-existence  of  some  other  rock  on  the  earth's  surface  as  the 
source  of  the  material  of  which  they  are  formed.  Igneous  rocks, 
on  the  other  hand,  must  have  come  from  beneath  the  surface, 
where  they  have  existed  from  all  time,  as  we  may  suppose. 
Believing  in  common  with  almost  all  geologists,  that  the 
earth  has  cooled  from  a  condition  of  intense  ignition,  we  of 
course  recognize  the  fact  that  there  was  a  time  when  all  exist- 
ing rocks  were  of  igneous  formation,  —  the  consolidated  crust  of 
the  earth  was  an  igneous  formation.  All  the  material  of  the 
sedimentary  rocks  must  have  come  from  this  source ;  but  it 
may  have  gone  through  several  cycles  of  change.  Igneous 
rock  has  been  ground  to  powder  and  deposited  in  water;  this 
material  has  been  again  broken  up  and  again  deposited  ;  and 
no  one  can  say  that  this  process  may  not  in  some  regions  have 
been  repeated  a  good  many  times. 

It  becomes  important,  then,  that  some  criterion  should  be 
established  by  which  the  eruptive  rocks  may  be  distinguished 
from  the  other  classes.  That  knowledge  of  this  kind  is  needed 
will  be  apparent  when  we  consider  that  the  conclusions  we 
have  to  draw  in  regard  to  the  dynamical  agencies  employed  in 
getting  the  rocks  into  their  present  condition  and  position  must 
depend  to  a  large  extent  on  the  origin  of  those  rocks.  For 
instance,  if  we  consider  a  certain  crystalline  mass  forming  the 
axis  of  a  chain  of  mountains  as  an  eruptive  rock,  our  conclu- 
sions in  regard  to  the  structure  of  that  chain  will  be  very 
different  from  what  they  would  be  if  we  considered  the  same 
material  as  simply  a  sedimentary  rock  which  has  assumed  a 
crystalline  texture  from  the  effects  of  metamorphic  action. 

Here,  then,  we  come  upon  another  of  the  difficulties  or 
discrepancies  of  opinion  among  geologists,  who,  starting  from 
the  theory  of  the  original  igneous  fluidity  of  the  earth,  begin 
almost  at  once  to  diverge  in  their  paths  towards  the  goal 
they  wish  to  attain,  which  is  nothing  more  nor  less  than 
the  solution  of  the  great  problems  of  dynamical  geology. 
"With  regard  to  the  rocks  which  have  come  to  the  surface 
from  beneath  during  the  tertiary  epoch,  and  which  we  call 
volcanic,  there  is  but  little  difference  of  opinion.  We  see 
them  now  issuing  from  volcanic  vents,  and  to  those  products 
of  massive  eruptions  which  precisely  resemble  in  texture  and 


82  Volcanism  and  Mountain-Building. 

composition  the  ejections  of  existing  volcanoes,  we  do  not  hesi- 
tate to  assign  a  similar  origin.  There  are,  however,  many  vari- 
eties of  rocks,  occurring  in  great  masses,  and  belonging  to  the 
older  epochs,  which  were  formerly  almost  universally  consid- 
ered to  be  eruptive,  and  in  regard  to  the  real  nature  of  which 
there  is  now  considerable  discussion  among  geologists.  These 
are  the  rocks  of  the  granitic  and  porphyritic  families.  Granite 
and  syenite  are  the  predominating  types  of  the  granitic,  and 
quartzose  porphyry  of  the  porphyritic  family.  These  are  the 
ancient  eruptive,  or  ancient  volcanic,  rocks  in  the  opinion  of 
many  ;  while  others  look  upon  them  as  having  been  originally 
sedimentary,  and  as  having  assumed  their  present  crystalline 
texture  through  the  influence  of  chemical  changes,  —  in  short, 
they  are  not  eruptive,  but  metamorphic.  By  those  who  adopt 
>  the  metamorphic  origin  of  granite  and  porphyry  the  argillaceous 
I  slates  are  supposed  to  have  furnished  the  material  for  the  first- 
\  named  of  these,  and  the  sandstones  for  the  other.  If  this  view 
were  correct,  we  should,  as  advocates  of  the  gradual  consolida- 
.'  tion  of  the  globe  from  a  condition  of  igneous  fusion,  be  placed 
in  a  difficult  position,  for  we  should  have  to  show  how  it  was 
that,  in  a  gradually  cooling  globe,  eruptive  material  was  not 
brought  to  the  surface  in  large  quantity  until  the  latest  epochs, 
when,  as  would  naturally  be  supposed,  the  crust  of  the  earth 
having  become  greatly  thickened  and  the  interior  sensibly 
cooled,  eruptive  action  would  have  diminished  instead  of  hav- 
ing increased.  To  avoid  this  difficulty,  some  of  the  chemical 
geologists  —  and  of  those  who  maintain  the  metamorphic  origin 
of  granite  such  are  indeed  the  only  consistent  ones  —  deny 
altogether  the  existence  of  any  primeval  eruptive  rock.  To 
them  all  visible  rocks  are  either  sedimentary,  or  they  have  been 
such ;  and  what  are  ordinarily  called  volcanic  and  eruptive 
masses  are  nothing  but  sedimentary  deposits  which  have  been 
softened  or  liquefied  by  the  internal  heat,  and  thus  enabled  to 
flow  as  lava.  The  idea  of  these  geologists  seems  to  be,  that 
the  series  of  changes  has  been  going  on  so  long  on  the  earth's 
surface  that  no  portion  of  the  original  crust  can,  by  any  possi- 
bility, remain  visible.  It  is  a  pushing  to  its  extremest  limits  of 
the  favorite  theory  of  Lyell,  that  no  traces  of  a  beginning  are 
to  be  found  ;  or,  at  least,  that  the  beginning  is  to  be  put  back 


Volcanism  and  Mountain-Building.  83 

as  far  as  possible,  and  that  all  geological  phenomena  are  to  be 
interpreted  with  that  one  idea  in  view,  the  result  being  that 
some  facts  have  been  extraordinarily  distorted  and  others 
overlooked,  for  the  purpose  of  making  things  pleasant  in  that 
direction.  Such  persons  as  wish  to  make  it  appear  that  no 
proofs  of  a  beginning  can  be  found  in  geological  facts  must 
go  still  further,  and  deny  that  the  earth  has  ever  been  in  a 
condition  of  igneous  fluidity,  from  which  it  has  been  gradually 
cooling  through  all  the  geological  ages.  They  are  trying  to 
pull  out  the  corner-stone  from  under  the  fabric  of  the  science. 

It  can  be  clearly  shown,  as  it  seems  to  us,  not  only  that  the 
volcanic  rocks  are  not  softened  or  metamorphosed  sedimentary 
materials,  but  that  the  same  is  true  of  the  rocks  of  the  granitic 
and  porphyritic  families  ;  these  are,  in  fact,  samples  of  the 
primeval  crust  of  the  earth,  such  as  it  was  before  any  sediment- 
ary  rocks  had  been  formed.  In  order  to  get  at  some  of  the 
proofs  of  this,  it  will  be  necessary  to  consider,  for  a  moment, 
the  mineralogical  composition  of  the  different  families  of  the 
eruptive  rocks  fihese  are  all  almost  exclusively  aggregates  of 
silicious  minerals,  including  among  them  silica  itself  or  quartz. 
Several  different  kinds  of  feldspars ;  hornblende  and  augite, 
two  very  closely  allied  minerals  ;  quartz ;  different  varieties  of 
mica  ;  magnetic  iron :  —  these  are  the  substances  of  which  all 
eruptive  rocks,  including  granite,  porphyry,  and  lava,  are 
almost  exclusively  made  up.  Quite  a  number  of  other  min- 
erals do  indeed  occur  in  them,  but  almost  always  in  very 
subordinate  quantity.  The  close  resemblance  in  external  I 
appearance  and  actual  composition  between  eruptive  rocks  \ 
from  different  parts  of  the  world  is,  indeed,  a  surprising  fact. 
But  it  is  more  surprising  still  to  find  that,  as  shown  by  the 
researches  of  the  great  chemist  Bunsen,  the  materials  of  which 
these  rocks  are  made  up  are  combined  in  certain  definite  pro-  < 
portions ;  so  that  if  we  determine  by  chemical  analysis  the 
quantity  of  any  one  of  the  ingredients  of  which  a  specimen  is 
composed,  we  can  by  mathematical  calculation  arrive  very 
nearly  at  the  amount  of  each  of  the  others.  The  "  law  of  Bun- 
sen,"  as  it  is  called,  is  of  the  greatest  possible  importance  in 
its  bearing  on  the  question  of  the  origin  of  the  eruptive  rocks. 
It  must  be  evident  to  all  that  this  law  could  not  be  true  if  the 


84  Volcanism  and  Mountain-Building. 

rocks  to  which  it  applies  were  of  metamorphic  origin.  If  that 
were  the  case,  and  they  were  really  derived  from  the  sediment- 
ary deposits,  they  could  not,  by  any  possibility,  fail  to  have  the 
same  varying  composition  which  these  sediments  themselves 
have,  and  which  can  by  no  means  be  brought  under  Bunsen's 
law. 

There  is  also  another  fact  which  has  a  most  important  bear- 
ing in  this  connection.  It  is  this  :  that  the  order  of  succession 
of  the  volcanic  rocks  has  been  the  same  all  over  the  world ; 
they  have  not  come  to  the  surface  in  different  regions  in  an 
indiscriminate  manner,  but  in  a  certain  sequence,  or  chrono- 
logical order.  This  extremely  important  fact  was  first  brought 
out  by  Richthofen,  who,  by  means  of  his  specially  good  oppor- 
tunities for  the  study  of  this  class  of  rocks,  was  enabled  to 
recognize  and  clearly  lay  down  this  order  of  succession,  and 
demonstrate  its  correctness  by  examples  collected  all  over  the 
globe.  The  chronological  order  of  succession,  as  well  as  the 
law  of  composii  ion  of  the  volcanic  rocks,  are  clearly  opposed  to 
the  idea  that  these  are  the  results  of  the  metamorpbism  of  the 
sedimentary  beds.  The  material  of  which  these  volcanic  ejec- 
tions are  made  up  must  have  come  from  beneath  the  shell  of 
sedimentary  deposits  ;  and  as  it  everywhere  came  from  beneath 
this  shell  in  a  certain  chronological  order,  so  it  must  ever  have 
previously  existed  there  in  the  same  order.  If  basalt  has  al- 
ways been  erupted  after  andesitic  lava,  then  basalt  must  have 
everywhere  formed  a  shell  of  material  underlying  andesite  in 
the  earth's  interior  ;  that  is  to  say,  the  mass  of  the  earth 
beneath  the  shell  of  sediments  is  formed,  for  a  certain  distance 
down,  of  layers  of  somewhat  different  material,  and  these  lay- 
ers are  arranged  in  a  similar  order  all  over  the  world.  What 
is  this  order  ?  Is  it  one  in  which  we  can  find  something  logi- 
cal, something  which  seems  to  be  connected  with  the  nature 
of  the  materials  themselves  ?  To  this  question  the  answer  is, 
in  a  general  way,  affirmative  ;  but  it  must  be  admitted  that  the 
processes  of  volcanism  are  so  complicated  that  we  cannot 
expect  an  agreement  in  all  minute  details,  but  only  in  the 
general  order  of  events,  looking  at  them  in  the  largest  way. 
It  will  not  do  to  study  up  the  exceptions  to  the  general  rule 
and  make  them  our  standards,  as  we  are  likely  to  do  if  we  con- 


Volcanism  and  Mountain- Building.  85 

fine  our  observations  to  any  one  locality.  We  are  rather  to 
try  and  get  the  general  principles  established,  and  then  en- 
deavor to  account  for  the  apparent  exceptions  in  a  manner 
which  will  be  in  harmony  with  the  general  well-established 
series  of  facts.  Thus,  if  it  can  be  shown  that  over  nine  tenths 
of  the  globe  the  order  of  succession  of  the  volcanic  rocks  is  one 
and  the  same,  then  let  this  fact  first  be  thoroughly  demon- 
strated, and  afterwards  let  the  exceptional  cases  in  the  remain- 
ing tenth  be  investigated,  each  on  its  own  merits,  in  its  ne- 
cessary subordination  to  the  general  law. 

In  something  like  this  spirit  the  investigations  of  Richthofen, 
in  regard  to  the  order  of  succession  of  the  volcanic  rocks,  must 
be  received.  It  is  not  claimed  that  he  has  clearly  made  out 
their  precise  sequence  in  all  localities  and  for  all  geological 
epochs  ;  but  that  there  is  a  certain  order  to  which  they  have 
conformed,  over  a  large  portion  of  the  earth,  and  especially  I 
during  the  tertiary  period,  can  no  longer  be  doubted ;  while  it  ' 
seems  probable  that  the  exceptions  which  do  occur  will  be 
found  to  be  of  comparatively  slight  importance,  and  that  all 
geologists  will  have  to  admit  the  value  of  these  investigations 
in  their  bearing  on  the  difficult  questions  to  which  they  are 
applicable. 

It  certainly  seems  clear  enough  that,  on  the  whole,  the  order 
in  which  the  volcanic  rocks  have  appeared  is  one  which  we  ) 
ought  to  have  expected,  if  the  theory  of  a  gradually  cooling 
globe  be  true.  The  more  silicious  and,  of  course,  the  lighter 
kinds  were  the  first  to  be  emitted  from  the  interior,  and  these 
have  been  succeeded  by  denser  or  more  basic  ones.  This  state- 
ment is  not  so  peculiarly  applicable  to  the  volcanic  as  it  is  to 
all  eruptive  rocks,  beginning  with  the  earliest  epochs  and  in- 
cluding the  granitic  family.  From  this  point  of  view  it  is  evi- 
dent that  quartzose  and  the  more  highly  silicious  rocks  prevailed 
almost  exclusively  during  the  earlier  periods,  and  that  they 
have  gradually  become  replaced  by  the  more  basic.  Granite 
and  syenite  were  once  the  predominating  eruptive  rocks ;  in 
the  latest  geological  ages  basalt  and  andesite  have  been. 

As  the  development  of  the  earth's  history  has  gone  on,  the 
regions  of  igneous  action  have  become  more  and  more  localized, 
and  we  have  now  only  eruptive  materials  issuing  from  craters 
7 


86  Volcanism  and  Mountain-Building. 

or  isolated  orifices  ;  the  days  of  massive  eruptions,  or  such  as 
took  place  from  fissures  of  great  length,  have  passed.  This  is 
as  we  should  expect ;  for,  although  there  are  some  who  follow 
the  school  of  Lyell  so  far  as  to  reject  everything  which  looks 
like  more  violent  action  of  any  kind  in  the  past  than  at  present, 
yet,  unless  we  admit  that  igneous  forces  were  more  .actively  at 
work  and  more  generally  disseminated  than  they  now  are,  we 
must  give  up  altogether  the  hypothesis  of  a  gradually  cooling 
globe  ;  and,  with  this  theory  gone,  we  are  entirely  afloat, —  ab- 
solutely destitute  of  any  guide  through  the  mazes  of  structural 
geology.  "We  must  admit  that  the  crust  has  been  constantly 
thickening,  while  the  cooling  has  been  going  on ;  and  if  this  has 
been  the  case,  the  facility  with  which  the  molten  matter  in  the 
interior  has  found  its  way  to  the  surface  must  have  been  con- 
stantly diminishing. 

There  is  a  point,  in  this  connection,  to  which  our  attention 
must  be  for  a  moment  turned.  There  is  a  difference  between 
the  granitic  and  the  ordinary  volcanic  rocks,  as  regards  the 
method  in  which  they  have  come  up  from  beneath,  dependent 
on  their  position  as  portions  of  the  exterior  shell  of  the  earth, 
in  consequence  of  which  the  former  have  more  of  an  intrusive, 
and  the  latter  rather  an  eruptive  character.  Forming,  as  it 
did,  the  original  surface  or  uppermost  layer,  granite  has  often 
been  raised  in  ridges,  before  any  sedimentary  rocks  existed, 
through  which  it  must  otherwise  have  been  obliged  to  force  its 
way.  There  being  no  resistance  from  the  weight  of  overlying 

/materials  to  be  overcome,  this  rock  could  assume  a  higher 
position  without  having  to  wait  for  tension  to  accumulate  so  as 

|  to  form  fissures,  as  has  been  the  case  with  the  more  recent 
eruptive  masses,  which  have  had  to  find  or  make  in  some 
manner  a  passage  through  a  considerable  thickness  of  the  con- 
solidated crust,  before  they  could  appear  upon  the  surface. 

The  real  character  of  granite  and  the  granitic  rocks  has 
been  much  discussed  of  late  among  chemists  and  geologists, 
the  former  adopting  usually  the  metamorphic  theory  of  its 
origin,  the  latter,  on  the  other  hand,  almost  all  taking  the  other 
side.  The  field  geologist  sees  these  rocks  occupying  a  position 
which  it  seems  impossible  that  they  should  have,  unless  they 
have  been  forced  upward  when  in  a  liquid  or  plastic  condition, 


Volcanism  and  Mountain-Building.  87 

and  he  observes  also  a  great  many  facts  which  preclude  the 
idea  that  this  liquidity  or  plasticity  has  originated  through 
metamorphic  action  on  sedimentary  materials.  And  in  a 
question  of  this  kind,  at  present  the  geological  facts  must  be 
allowed  a  greater  weight  than  the  chemical,  since  chemistry 
has  thus  far  proved  to  be  rather  a  blind  guide  to  those  en- 
deavoring to  unriddle  the  mysterious  reactions  of  the  prime- 
val earth.  That  the  peculiar  texture  of  granite,  as  compared 
with  that  of  the  volcanic  rocks  proper,  does  present  a  difficulty, 
there  is  no  doubt ;  but  if  we  consider  that  this  rock,  forming 
as  it  did  the  exterior  crust,  must  have  been  in  much  closer 
proximity  to  the  ocean  than  were  the  underlying  masses,  we 
shall  have  no  difficulty  in  understanding  that  a  larger  amount  ( 
of  water  and  a  lower  temperature  were  conditions  which  exer-3  ^ 
cised  a  powerful  influence  in  determining  its  texture. 

There  can  be  no  doubt,  then,  that  the  seat  of  volcanic  action 
has  gradually  receded  from  the  exterior  towards  the  centre, 
and  that  in  so  receding  it  has  descended  into  regions  of  denser 
material,  and  that  these  regions  have  been  reached  in  the  same 
order  in  different  parts  of  the  world,  showing  that  the  arrange- 
ment of  the  materials  of  the  crust  is  everywhere  strikingly 
similar. 

We  have  an  important  and  difficult  question  to  answer  in 
endeavoring  to  ascertain  the  nature  of  the  force  which  brings 
the  material  of  the  molten  interior  to  the  surface.  This  is  a 
subject  which  has  been  passed  over  without  discussion  by  some 
writers,  while  others  have  given  it  a  measure  of  consideration, 
usually  making  it  evident  by  their  treatment  of  it  that  they  felt 
its  difficulties.  It  used  formerly  to  be  supposed  that  the  open- 
ing of  a  fissure  in  the  earth's  crust  would  necessarily  cause  the 
molten  material  below  to  issue  forth  without  further  cause. 
The  insufficiency  of  this  as  a  reason  has  been  felt  by  the  later 
writers  ;  but  of  those  discussing  the  subject  hardly  any  two 
have  been  agreed  in  their  views.  Sometimes  the  differences  of 
opinions  thus  disclosed  are  not  radical ;  but  usually  they  are, 
and  in  a  good  many  instances  we  find  authors  diametrically 
opposed  to  each  other.  In  one  respect  there  is  a  fair  amount 
of  agreement  among  the  theorizers  on  volcanic  phenomena. 
Almost  all  consider  the  access  of  water  as  essential,  in  some 


88  Volcanism  and  Mountain-Building. 

way  or  other,  to  the  emission  of  lava.  But  in  regard  to  the 
modus  operandi  of  the  water  and  the  manner  in  which  it  is  to 
find  its  way  down  to  the  volcanic  focus,  most  authors  are  found 
to  preserve  a  discreet  silence.  Mr.  David  Forbes,  whose  lec- 
tures and  writings  on  these  subjects  have  been  much  circulated 
of  late  in  the  English  magazines,  says  that  all  which  is  required 
to  account  for  the  phenomena  of  volcanic  action  is  "  the  assump- 
tion that  water  from  the  sea  should,  by  some  means  or  other ,  find 
its  way  down  into  the  reservoir  of  molten  matter  beneath  the 
surface  "  ;  what  the  means  are  by  which  the  water  is  to  gain 
access  to  the  interior  are  not  given,  nor  is  the  mode  in  which 
the  water  acts  after  it  has  reached  the  depths  anywhere  ex- 
plained. Scrope,  who  was  among  the  first  of  modern  authors 
to  advocate  the  necessity  of  water  as  an  agent  in  volcanic  erup- 
tions, solves  the  difficulty  in  a  most  curious  manner,  namely, 
(  by  supposing  the  water  to  be  already  present  in  the  material 
?  which  is  to  issue  forth  as  lava,  and  only  waiting  to  be  vaporized 
whenever  a  transfer  of  heat  into  the  region  takes  place.  To  use 
1  the  words  of  that  author,  "It  is  now  generally  recognized  that 
the  power  which  forces  up  lava  from  a  depth  of  miles,  through 
narrow  and  crooked  fissures  broken  across  the  solid  crust  of 
the  globe  is  no  other  than  steam,  developed  in  the  interior  of  the 
lava  by  vaporization  of  water  intimately  disseminated  through- 
out its  substance."  Professor  Phillips,  one  of  the  most  cau- 
tious of  the  English  writers  on  geology,  in  his  latest  work  on 
Vesuvius,  quoted  in  a  previous  article,  incidentally  alludes  to 
water  as  a  cause  of  "  volcanic  excitement,"  as  he  terms  it,  but 
goes  no  further  in  that  direction. 

The  eminent  chemical  geologist,  Bischof,  is  the  only  author 
who  has  gone  into  anything  like  an  elaborate  discussion  of  the 
manner  in  which  water  might  gain  access  to  the  molten  inte- 
rior and  act  as  a  motive-power  in  the  ejection  of  the  lava.     He 
perceives  some  of  the  difficulties  in  the  way  of  the  adoption  of 
,    this  idea,  and  endeavors  to  remove  them.     It  seems  pretty 
clear  that  steam  at  its  maximum  elastic  force  would  not  have 
power  enough  to  raise  a  column  of  lava  from  the  region  from 
'.    which  it  is  supposed  to  come  up  to  the  summit  of  even  a  mod- 
f  erately  high  volcano.     This  difficulty  Bischof  gets  over  by  sup- 
/  posing  that  the  column  of  lava  has  lengths  of  steam  included 


Volcanism  and  Mountain-Building.  89 

in  it,  like  the  bubbles  of  air  in  a  barometer  tube.  This  ex-  . 
planation  is  also  adopted  by  Lyell,  who  follows  Bischof  closely  • 
in  all  that  relates  to  the  theory  of  volcanic  action.  This  hy- 
pothesis, moreover,  clearly  involves  another  difficulty,  which 
is  this :  that  two  columns,  one  of  water  and  the  other  of  lava, 
must  be  in  communication  with  the  molten  mass  of  the  interior 
of  the  earth,  and  yet  that  the  elastic  force  of  the  steam  gener- 
ated by  that  water  shall  throw  out,  not  the  water  itself,  but  the 
lava.  It  is  believed  by  some  physicists  that  it  may  be  possible 
for  water  to  pass  through  minute  fissures,  through  which  it 
cannot  return  when  converted  into  steam,  although  this  has 
not  yet  been  clearly  demonstrated.  But,  even  admitting  this, 
it  does  not  appear  how  it  is  that  the  force  of  the  steam  is  used  to 
lift  up  the  column  of  lava  to  a  height  of  ten,  fifteen,  or  even 
twenty  thousand  feet  above  the  level  at  which  the  water  enters, 
rather  than  to  blow  out  the  fissured  and  necessarily  much  weak- 
ened thinner  portion  of  the  crust  through  which  the  water  has 
found  its  way.  This  objection  is  an  insurmountable  one,  in  our 
judgment ;  and,  indeed,  the  assumption  that  steam  is  fheprimum 
mobile  in  all  volcanic  eruptions  is  one  beset  with  difficulties. 
No  theory  of  volcanoes  can  be  adopted  that  will  not  account ? 
for  the  phenomena  of  massive  eruptions  as  well  as  for  ejections 
from  crateriform  orifices,  and  this  the  water  theory  is  obviously 
incompetent  to  do.  That  water  comes  into  play  in  volcanic 
eruptions  there  can  be  little  doubt ;  but  this  is  in  the  later  • 
stages  of  the  process,  when  cinders  and  ashy  materials  are  " 
chiefly  ejected.  And  it  is  by  no  means  certain  that  the  rain' 
may  not  be  quite  as  competent  as  the  sea  to  supply  the  neces- 
sary water.  Much  stress  has  been  laid  on  the  fact  that  most 
volcanoes  are  near  the  sea  or  on  islands,  as  going  to  prove  that 
eruptive  action  cannot  take  place  without  the  presence  of  sea- 
water.  But  it  must  be  recollected  that  this  nearness  is,  in 
many  cases,  only  comparative,  with  reference  to  the  total 
breadth  of  the  continent,  and  not  absolute.  Thus  the  volcanoes 
of  the  South  American  Andes  are,  in  many  instances,  two  hun- 
dred to  three  hundred  miles  from  the  sea,  which  is  certainly  a 
long  distance  for  action  to  be  transmitted  laterally  through 
the  intervening  rock.  Besides,  there  are  not  a  few  regions 
where,  within  a  recent  geological  period,  if  not  during  the 


90  ]  Volcanism  and  Mountain- Building. 

present  epoch,  volcanic  action  has  taken  place  on  a  large  scale, 
at  a  great  distance  from  the  sea,  at  a  high  altitude  above  it,  and 
also  far  from  any  inland  waters  of  magnitude,  which  might  be 
supposed  to  answer  instead  of  the  ocean  as  feeders  to  the  vol- 
canic excitement.  We  need  only  instance,  in  this  connection, 
the  line  of  volcanoes  which  extends  across  our  continent  through 
Northern  Arizona  and  New  Mexico,  of  which  Mount  San  Fran- 
cisco and  Mount  Taylor  are  the  dominating  summits. 

Everything  indicates  that  we  cannot  separate  the  agencies 
which  give  rise  to  the  formation  of  mountain  chains  from  those 
which  are  energetic  in  volcanic  eruptions.  Whatever  cause  is 
capable  of  folding  the  crust  of  the  earth  into  ridges,  or  thrust- 
ing a  portion  of  it  up  above  the  adjacent  parts,  is  also  compe- 
tent, if  carried  a  little  further,  to  produce  a  fissure,  and  through 
this  the  underlying  material,  whether  it  be  in  a  fluid,  plastic,  or 
viscous  condition,  may  be  forced,  by  the  pressure  arising  from 
the  subsidence  of  that  portion  of  the  crust  which  borders  it  on 
one  side  or  the  other. 

y  We  have,  therefore,  to  go  back  another  step  and  endeavor 
to  ascertain  what  the  forces  are  which  have  been  active  in  pro- 
ducing those  ridges  of  the  earth's  surface  which  we  call  moun- 
tains. A  mountain  may  result  either  from  a  positive  elevation 
of  the  mass,  or  from  depression  of  the  adjacent  region.  We 
leave  out  of  view  here  those  elevations  which  have  their  origin 
simply  in  denudation  or  erosion  by  water  of  the  surrounding 
surface,  for  these  are  easily  understood  and  comparatively 
unimportant.  It  is  true  that  we  have  absolutely  no  means 
of  ascertaining  how  much,  in  the  past  geological  ages,  of  the 
elevation  of  our  mountain  chains  is  due  to  actual  upheaval  or 
increase  of  distance  from  the  centre  of  the  earth,  and  how 
much  to  depression  of  other  portions  of  the  surface.  We  are 
accustomed  to  refer  all  elevations  to  the  level  of  the  sea  as  a 
zero,  but  we  have  no  reason  to  suppose  that  this  level  has  itself 
been  invariable  ;  that  is  to  say,  it  cannot  be  taken  for  granted 
that  the  distance  from  the  centre  of  the  earth  to  the  sea-level 
at  any  particular  point  on  the  earth's  surface  has  always  re 
mained  the  same.  On  the  contrary,  there  is  abundant  evidence 
that  the  sea-basins  have  deepened  since  the  earlier  geological 
periods ;  but  of  the  extent  to  which  the  sinking  of  the  sea-level 


Volcanism  and  Mountain- Building.  91 

which  would  thus  be  produced  has  been  compensated  by  an  <, 
increase  of  the  area  of  the  land,  we  can  only  form  the  crudest  j 
conjecture.     "We  do  not  yet  know  the  depth  of  the  deepest 
portions  of  the  ocean,  or  where  they  are  situated. 

Looking  at  the  surface  of  the  earth  simply  with  reference  to 
continental  and  oceanic  areas,  we  have  reason  to  believe  that 
the  differences  of  level  between  them  are  the  result  of  depres- 
sion rather  than  of  elevation.  The  masses  which  now  form  the 
continents  have  been  left  where  they  were,  while  the  ocean 
beds  have  sunk  and  allowed  the  water  to  retire  from  the  more 
elevated  portions.  This  follows,  indeed,  necessarily,  from  the 
nature  of  the  assumed  cause  of  differences  of  elevation,  namely,  j 
the  shrinkage  of  the  interior,  and  the  endeavors  of  the  crust  to 
adapt  itself  to  the  diminished  nucleus.  If  we  conceive  that  the 
globe,  as  a  whole,  shrinks  somewhat  unevenly,  and  it  is  hardly 
possible  to  conceive  that  it  should  be  otherwise,  since  neither 
ther  composition  of  the  cooling  body  nor  its  rate  of  parting  with 
its  heat  would  be  likely  to  be  entirely  uniform  in  all  its  parts, 
then  the  region  in  which  positive  elevations  would  be  likely  to 
take  place  would  be  the  borders  of  the  most  rapidly  shrinking 
area,  or  where  it  joins  on  to  the  portion  which  remains  compar- 
atively stationary.  These  more  rapidly  shrinking  areas  would, 
of  course,  be  the  ocean  beds,  and  the  stationary  area  the  conti 
nental  masses,  while  the  edges  of  the  continents  would  be  the 
region  of  positive  uplift  or  of  mountain  formation.  This  is  the 
basis  of  Professor  Dana's  theory  of  the  formation  of  continents, 
as  set  forth  by  him  in  the  "  Geology  of  the  Exploring  Expedi- 
tion "  and  elsewhere,*  and  of  which  a  synopsis  was  given  by 
us  in  this  Eeview  some  twenty  years  ago.  The  investigations 
of  geologists  have,  since  that  time,  given  additional  value  and 
lustre  to  these  lofty  generalizations  of  Professor  Dana's,  in  the 
opinion  of  the  writer  of  this  article,  although  it  must  be  ad- 
mitted that  they  have  not  met  with  general  adoption.  Other 
theories  have  been  suggested  and  discussed,  but  without  any 
very  definite  conclusions  having  been  arrived  it ;  at  all  events, 
the  conclusions  reached  have  rarely  been  satisfactory  to  others 
than  their  authors.  A  great  mass  of  material  has  been  gath- 
ered bearing  on  the  structure  of  mountain  chains,  or,  at  least, 

*  See  references  on  page  79.  f 


92  Vblcanism  and  Mountain-Building. 

capable  of  being  made  available  in  that  direction ;  but  little  has 
been  accomplished  in  the  way  of  applying  this  information  to 
the  working  out  of  any  theory  of  mountain  building.  What  the- 
ories have  been  suggested  have  been  of  the  vaguest  kind,  and, 
in  some  instances,  facts  have  been  entirely  ignored  in  support- 
ing them. 

While  believing,  with  Professor  Dana,  that  mountain-build- 
ing is,  to  a  large  extent  at  least,  the  result  of  an  antagonism 
between  subsiding  and  stationary  masses  of  the  earth's  crust, 
we  are  fully  aware  this  is  a  somewhat  vague  way  of  stating  the 
case,  and  that  a  more  detailed  account  of  the  agencies  at  work 
in  this  operation,  and  of  the  methods  in  which  they  act,  is  ex- 
tremely desirable.  But  when  we  come  to  examine  what  is 
known  of  the  detailed  structure  of  the  great  mountain  chains 
of  the  world,  we  find  that,  in  spite  of  all  that  geologists  have 
done,  our  information  is  exceedingly  defective.  In  the  chain 
of  the  Alps  it  is  true  that  we  have  a  great  many  local  sections 
in  the  works  of  Giimbel,  Favre,  Studer,  and  especially  of  the 
geologists  of  the  Austrian  official  survey,  the  Reichsanstalt. 
But  how  deficient  are  our  generalized  sections  across  the  entire 
chain !  Indeed,  there  is  not  one  on  a  large  scale  from  which 
an  idea  of  the  structure  of  the  mass,  as  a  whole,  can  be  obtained. 
And  if  this  be  true  for  the  Alps,  how  much  more  is  it  likely  to 
be  so  for  the  great  chains  of  Asia  and  of  America,  which,  in 
comparison  with  the  much  visited  and  studied  European  moun- 
tain masses,  are  almost  unknown.  Indeed,  it  is  only  quite  re- 
cently that  the  subdivisions  of  our  own  Cordilleras,  grand  as 
they  are,  began  to  be  indicated  on  our  maps  or  even  to  receive 
names.  And  not  even  so  far  as  that  has  our  knowledge  of  the 
Asiatic  chains  of  mountains  reached.  Of  that  vast  region  north 
of  the  main  Himalayan  range,  on  which  €ire  piled  the  masses 
of  the  Kun-Liin,  the  Karakorum,  and  others,  we  know  as  yet 
almost  nothing,  so  far  as  geological  structure  is  concerned. 
Even  the  sections  which  the  India  survey  gives  of  the  middle 
and  lower  Himalayan  ranges  are  on  a  small  scale  and  difficult 
to  unriddle.  Generalizations  in  regard  to  mountain  structure 
at  the  present  time,  which  profess  to  go  into  some  detail,  must, 
therefore,  be  drawn  with  much  caution,  and  taken  rather  as 
indicating  the  direction  in  which  future  and  much-needed 


Volcanism  and  Mountain  Building.  93 

work  may  be  accomplished,  and  not  as  based  on  anything 
completed. 

Of  all  mountain  forms,  the  simplest  are  those  which  result 
from  denudation.  Masses  of  rock  are  often  left  standing,  iso- 
lated from  each  other  by  the  removal  of  the  adjacent  material 
through  the  action  of  water ;  and  these  masses,  where  the  ero- 
sion has  been  extensive  and  long  continued  and  in  suitable 
strata,  are  occasionally  so  large  as  properly  to  be  called  moun- 
tains. There  are  fine  examples  of  the  forms  resulting  from 
erosion  in  our  Rocky  Mountain  region  and  farther  west.  But 
erosion  on  a  large  scale  cannot  take  place  without  continental 
elevation.  There  must  be  a  rapid  inclination  of  the  surface 
towards  the  sea  to  admit  of  portions  of  the  surface  being  deeply 
cut  into  by  the  streams  which  traverse  it.  Hence  the  forma- 
tion of  mountains  by  erosion  is  rather  to  be  regarded  as  a 
secondary  operation,  and  as  a  sort  of  carving  of  an  already 
elevated  mass  into  detached  portions  which  may  then  bear 
the  name  of  mountains,  which,  previous  to  the  erosion,  the 
whole  would  have  been  called  simply  a  plateau.  The  Book 
Mountains  in  Colorado  are  admirable  instances,  on  a  grand 
scale,  of  this  mode  of  formation. 

The  next  most  simple  form  of  mountain  building  is  that  in 
which  masses  of  rock  —  and  it  is  chiefly  the  sedimentary  forma- 
tions which  are  thus  acted  on  —  are  broken  across  and  tilted 
up  at  an  angle,  from  an  unequal  subsidence  of  the  fractured 
portions  ;  something  as  we  see  happening  in  the  ice  covering  the 
surface  of  a  lake  when  it  has  been  broken  up  by  the  waves  and 
then  frozen  together  again,  the  different  pieces  being  inclined 
to  each  other  at  slight  angles,  instead  of  lying  all  in  one  plane 
as  before.  Such  mountains  are  not  usually  developed  on  a 
large  scale,  for  in  almost  every  case,  if  there  is  a  fissure  formed, 
there  is  an  outpouring  of  eruptive  material. 

If,  on  the  other  hand,  the  group  or  series  of  strata,  instead 
of  being  broken  across  and  tilted,  are  gradually  bent,  then  a 
ridge  or  protuberance  of  the  surface  will  be  formed,  and  it  will 
have,  of  course,  various  degrees  of  curvature.  A  series  of  such 
ridges  will  alternate  with  relatively  depressed  regions  or  val- 
leys, the  whole  forming  a  system  of  foldings  which  are  very 
likely  to  be  parallel  or  nearly  so,  because  parallelism  in  this 


94  Volcanism  and  Mountain-Building. 

case  merely  means  a  persistence  of  the  bending  agencies  in 
one  direction.  Such  a  system  of  parallel  ridges,  or  folds  may 
be  seen  in  the  Appalachians  and  the  Jura,  two  perfectly  typical 
regions  in  this  respect.  But  these  may  not,  by  any  means,  be 
taken  as  representatives  of  all  mountain  chains,  as  has  been 
done  by  Hall  and  H.  D.  Rogers.  On  the  contrary,  they  are 
only  chains  of  the  second  or  third  order  of  magnitude,  so  far 
as  elevation  is  concerned,  and  in  many  respects  exceptional. 
They  are,  so  far  as  we  know,  the  only  systems  of  mountains, 
having  great  geographical  development,  in  which  there  has  been 
no  emission  of  eruptive  material  from  below  and  no  extensive 
metamorphism. 

It  seems  to  be  clearly  indicated  by  the  results  of  geological 
investigations,  that  the  great  mountain  chains  of  the  world 
have  been  blocked  out  —  if  the  use  of  such  a  phrase  may  be 
permitted  —  from  the  earlier  geological  times,  and  often  from 
the  earliest.  Their  structure  shows  most  distinctly  that  their 
development  has  been  a  gradual  one.  But  it  was  not  always 
the  case  that  this  development  was  continued  down  to  the 
latest  period.  On  the  contrary,  many  chains  have  ceased  to 
grow  after  attaining  a  certain  elevation  ;  and,  having  ceased  to 
be  influenced  by  forces  acting  from  beneath,  they  have  ever 
since  been  subjected  to  those  erosive  agencies  which  constantly 
tend  to  plane  down  the  inequalities  of  the  surface.  Hence, 
the  highest  chains  contain  the  most  recent  geological  forma- 
tions. The  Himalaya,  the  Alps,  the  Andes,  the  Cordilleras,  — 
these  are  the  great  chains  of  the  world,  and  these  are  all  made 
up,  in  part  at  least,  of  the  newest  formations.  The  Ural, 
the  Scandinavian  Mountains,  the  Appalachians,  the  Brazilian 
ranges,  —  these  are  examples  of  mountain  chains  which  have 
ceased  to  grow  at  a  comparatively  early  geological  period, 
and  within  whose  masses  no  modern  rocks  can  be  found. 

The  results  of  modern  investigations,  especially  in  the  Andes 
and  Cordilleras,  are  diametrically  opposed  to  the  theories  of 
Elie  de  Beaumont,  on  which  he  has  spent  so  much  labor,  and 
which  he  has  built  up  with  such  care  and  such  an  outlay  of  math- 
ematical calculations.  According  to  the  views  of  this  eminent 
French  geologist,  the  earth  in  cooling  and  contracting  has  de- 
veloped its  mountain  ranges  along  lines  which  are  parts  of  great 


Volcanism  and  Mountain-Building.  95 

circles .  drawn  about  the  globe  in  a  network  of  curves  developed 
symmetrically  from  the  points  where  a  solid  with  regular 
pentagonal  faces  included  within  the  earth  would  touch  its 
surface.  It  is  also  a  part  of  De  Beaumont's  system,  that  moun- 
tain chains  having  the  same  direction  must  be  of  the  same  geo- 
logical age  ;  so  that  law,  order,  and  crystalline  harmony  would 
seem  to  be  clearly  established  in  what  would  otherwise  seem 
almost  a  chaos  of  facts,  if  these  theories  should  bear  the  test  of 
close  examinations,  and  found  to  be  applicable  all  over  the  globe. 
So  desirable  was  this,  that  it  is  no  wonder  that  many  geologists 
were  glad  to  become  converts  to  these  views.  One  by  one  they 
have  dropped  off,  however ;  and  few  excepting  Frenchmen  are 
now  found  upholding  the  theory  of  the  pentagonal  network. 
Many'  years  of  labor  among  mountains  of  the  first  rank  have 
convinced  us  that  the  real  facts  are  almost  exactly  in  opposi- 
tion to  Elie  de  Beaumont's  views.  Instead  of  its  being  true 
that  identity  of  direction  in  mountain  chains  implies  identity  of 
geological  age,  one  might  almost  say  that  just  the  opposite  is 
true.  Certain  it  is,  that  the  great  mountain  chains  are  made- 
up  of  distinct  portions,  which  have  similar  directions  and  very 
different  geological  ages.  Thus,  in  the  Andes  and  Cordilleras, 
we  have  one  grand  system  of  mountains  made  up  of  an  aggre- 
gation of  many  different  parts,  each  having  approximately  the 
same  direction,  and  each  of  these  parts  or  sections  being  the 
result  of  a  series  of  geological  changes  which  have  been  going 
on  through  all  the  epochs,  from  the  earliest  to  the  latest. 

Take,  for  instance,  the  widest  portion  of  the  whole  belt  of 
mountains  which  forms  the  western  side  of  the  American  con- 
tinent, or  that  between  the  thirty-sixth  and  fortieth  parallels  of 
north  latitude.  We  have  here  a  mass  of  ranges  fully  a  thou- 
sand miles  in  width,  having  a  certain  unity  which  cannot  be 
disputed,  and  yet  made  up  of  parts  which  have  been  growing 
on  to  each  other  ever  since  the  azoic  period.  For,  even  at 
that  earliest  geological  epoch,  the  chain  of  the  Rocky  Moun- 
tains was  marked  out,  and  each  successive  period,  down  even 
to  the  very  latest,  has  seen  some  additions  made  to  the  mass. 

In  all  great  and  complicated  chains  of  mountains,  almost 
without  exception,  we  find  eruptive  rocks  forming  a  portion  of 
the  mass ;  these  may  be  either  ancient  or  modern,  or  both  to- 


96  Volcanism  and  Mountain-Building. 

gether.  Great  chains  almost  invariably  are  made  up,  to  a  large 
extent,  of  granitic  rocks ;  usually  granite  itself  forms  the  bulk 
of  the  mass.  Yolcanic  overflows  may  or  may  not  occur ;  dif- 
ferent chains  differ  very  much  in  this  respect.  The  granite 
usually  forms  the  central  and  higher  portion  of  a  great  chain  ; 
it  is  a  remarkable  exception  when  this  is  not  the  case.  In  the 
Alps,  while  the  bulk  of  the  central  masses  are  of  a  granitic 
character,  there  are  a  few  very  lofty  and  almost  isolated  points 
or  even  large  domes  made  up  of  sedimentary  materials,  as,  for 
instance,  the  Matterhorn,  and  some  of  the  very  highest  portions 
of  the  Bernese  Oberland.  In  the  Himalayas  the  main  portions  of 
the  higher  ranges  seem  to  be  granite,  but  data  are  extremely 
deficient  for  those  regions.  Eruptive  rocks,  both  of  the  gra- 
nitic and  volcanic  types,  are  abundantly  but  very  unequally  dis- 
seminated through  the  great  ranges  which  make  up  the  Pacific 
edge  of  North  and  South  America.  The  Andes  are  very  largely 
made  up  of  volcanic  materials  piled  on  each  other  to  an  im- 
mense height ;  these  appear  to  predominate  over  the  granitic  ; 
but  different  portions  of  the  chain  are  very  unequally  situated 
in  this  respect.  The  same  is  true  with  regard  to  the  North 
American  Cordilleras ;  here,  vast  masses  of  granitic  rocks 
forming  exclusively  all  the  more  elevated  ranges ;  there,  vol- 
canic materials  covering  up  all  the  others,  and  far  exceeding 
them  in  quantity. 

When  the  study  of  orography  was  in  its  infancy,  it  was 
thought  that  the  typical  form  of  mountain  ranges  was  that 
of  a  mass  or  wedge  of  granite  thrust  up  from  beneath  and 
carrying  with  it  the  sedimentary  rocks  through  which  it  had 
made  its  way,  which  would  then  be  symmetrically  disposed 
upon  the  central  mass,  the  stratified  beds  dipping  each  way 
from  it,  and  forming  what  geologists  call  an  anticlinal  axis. 
It  was  found,  after  more  accurate  observations  began  to  be  made 
than  were  customary  in  the  early  days  of  geology,  that  the 
structure  of  most  of  the  great  chains  was  by  no  means  so  sim- 
ple as  this,  and,  consequently,  some  hastened  to  conclude  and 
to  state  that  no  such  thing  had  ever  occurred  at  all.  Some 
even  went  to  such  an  extreme  in  the  opposite  direction  as  to 
maintain  that  all  mountains  had  a  structure  exactly  the  reverse 
of  the  anticlinal,  namely,  synclinal.  Of  this  theory  more  pres- 


Volcanism  and  Mountain-Building.  97 

ently  ;  it  must  be  considered  in  connection  with  that  which 
makes  granite  and  all  the  granitic  rocks  to  be  of  sedimentary 
origin,  and  not  eruptive,  but  metamorphic. 

Believing,  as  we  do,  that  granite  or  some  rocks  of  the  gra- 
nitic family  formed  the  original  exterior  crust  of  the  earth,  it  is 
not  difficult  for  us  to  understand  that  these  must  necessarily 
form  the  core  of  most  mountain  chains,  and  that  especially  it 
must  predominate  in  those  which  reached  their  full  develop- 
ment during  the  earlier  geological  ages.  When  the  ridging  or 
wrinkling  of  the  crust  began  to  take  place,  granite,  being  the 
uppermost  layer,  was  raised  into  the  highest  position,  and  might 
be  elevated  to  almost  any  amount,  provided  the  base  on  which 
the  protuberance  was  raised  was  broad  enough.  Circumstances, 
the  exact  nature  of  which  it  would  not,  in  the  present  state  of 
our  knowledge,  be  easy  to  state  in  detail,  have  differently  influ- 
enced the  different  ranges  in  regard  to  the  point  whether  the 
granite  crust  should  be  entirely  broken  through  and  the  under- 
lying more  basic  rocks  be  brought  to  the  surface.  In  the  Andes 
and  Cordilleras,  everywhere  the  eruption  of  the  granite  has 
been  followed,  at  some  stage  of  the  mountain-building  pro- 
cess, by  the  outpouring  of  volcanic  rocks,  beginning  with  pro- 
pylite  and  andesite  and  ending  with  basalt.  We  know  too  little 
of  the  structure  of  the  great  South  American  chain  as  yet ;  but 
it  is  certain  that  modern  volcanic  rocks  form  a  large  portion 
of  it,  and  that  granite  lies  at  the  bottom  of  the  whole,  although 
subordinate  in  quantity,  at  least  through  considerable  portions 
of  the  chain.  In  North  America  the  granite  predominates,  on 
the  other  hand,  and  the  volcanic,  although  crowning  the  range 
in  many  places,  is,  on  the  whole,  much  inferior  in  bulk  to  the 
more  ancient  eruptive  masses.  This  relation  is  changed,  how- 
ever, as  we  go  north,  and  in  Oregon  basaltic  lava  covers 
almost  the  whole  of  the  Cascade  Range,  and  has  flowed  far 
and  wide  over  the  adjacent  country.  Striking  as  is  the  pre- 
dominance of  volcanic  rocks  in  the  mountain  ranges  which 
encircle  the  Pacific,  it  is  still  more  extraordinary  to  find  them 
almost  wholly  absent  in  the  High  Alps,  and  in  the  Himalayas 
so  far  as  yet  ascertained,  while  abundantly  exhibited  both  north 
arid  south  of  these  ranges.  Thus  the  vast  lava  plains  of  the 
Dekkan  lie  to  the  south  of  the  Himalayas,  while  to  the  north 


98  Vblcanism  and  Mountain- Building. 

extensive  volcanic  formations  are  also  reported ;  but  so  little  is 
accurately  known  of  that  region,  that  it  is  hardly  possible  to  say 
whether  there  are  any  traces  of  active  volcanism  there.  The 
volcanic  formations  of  Europe  lie  to  the  north  and  south  of  the 
Alps,  at  a  considerable  distance,  as  any  one  may  see  by  con- 
sulting a  geological  map  of  that  country.  The  best  solution 
which  can  be  offered  for  this  problem  of  the  unequal  distribu- 
tion of  volcanic  rocks  on  the  two  opposite  continental  masses 
is,  that  in  Europe-Asia  the  thickness  of  the  granitic  crust  was 
greater  than  on  the  American  side,  so  that  the  underlying  vol- 
canic masses  could  not  find  their  way  to  the  surface  through  the 
uplifted  protuberance,  but  only  at  its  edges,  where  tension  was 
great  and  the  thickness  of  the  granitic  layer  less  than  towards 
the  centre  of  the  uplift.  That  this  may  have  been  the  case  is 
indicated  by  the  much  greater  extent  of  the  land  mass  of  the 
continent  of  Europe-Asia,  the  greater  absolute  height,  and  the 
vastly  greater  breadth  of  the  ranges  taken  as  a  whole.  When 
these  die  out,  then  the  volcanic  rocks  come  in,  as  to  the  south 
of  the  Caucasus  and  in  the  space  between  that  chain  and  the 
western  extremity  of  the  Himalayan  ranges.  It  is  not  without 
a  meaning  in  this  connection  that,  as  it  appears,  the  phenom- 
ena of  absolute  elevation  have  been  continued  up  to  a  later 
geological  period  in  the  chains  bordering  the  Pacific  than  in 
that  region  which  includes  the  Alps  and  the  Himalayas. 

The  mechanism  by  means  of  which  simple  upheavals,  up- 
lifts, or  downthrows  of  portions  of  the  stratified  shell  of  the 
globe  are  accomplished  is  not  difficult  to  be  comprehended. 
But,  to  explain  the  origin  of  so  complicated  a  series  of  folds 
as  that  exhibited  by  the  Jura  and  the  Appalachians,  where  there 
is  no  central  axis  of  crystalline  or  eruptive  rock,  is  a  more  diffi- 
cult task.  Among  the  theories  proposed  to  that  end,  that  of 
Professor  H.  D.  Rogers  is  the  wildest  and  most  fantastic.  Ac- 
cording to  this,  it  was  the  pulsation  of  earthquake  waves  through 
the  molten  interior  of  the  earth  which  laid  the  superficial  crust 
in  plaits.  As  this  idea  has  never  met  with  acceptance  on  the 
part  of  any  sober-minded  worker  in  geology,  it  need  only  be 
alluded  to  here.  If  it  had  not  been  elaborated  with  so  much 
care  and  brought  forward  on  so  many  occasions  by  its  author, 
it  would  have  seemed  as  if  rather  intended  to  be  classed  with 


Volcanism  and  Mountain-Building.  99 

that  half-playful  hint  of  Sir  John  Herschel's,  that  the  heat  of^ 
the  sun  is  kept  up  by  monstrous  organized  existences,  whose 
dim  outlines  are  revealed  to  us  in  the  willow-leaf  structure  of" 
the  surface  of  our  "  ruler,  fire,  light,  and  life,"  as  Mr.  Proctor 
calls  the  centre  of  our  planetary  system.  There  is  nothing 
about  Professor  Rogers's  theory  which  will  bear  the  test  of 
examination.  It  has  not  the  slightest  adaptation  to  chains 
which  are  unlike  the  Appalachians  in  structure,  and,  as  already 
stated,  this  range  and  the  Jura  are  quite  exceptional  in  char- 
acter. From  it  we  get  no  clue  as  to  how  the  waves  originated ; 
how  they  were  propagated  from  one  side  only,  as  would  be  re- 
quired to  meet  the  case  of  the  structure  of  the  Appalachians ; 
how  the  strata,  instead  of  being  shattered  in  pieces  by  the  rapid 
pulsations  of  the  internal  fluid,  were  gradually  bent  in  such  a 
manner  as  could  only  have  been  accomplished  by  very  long- 
continued  action  ;  how  the  corrugated  crust  was  held  in  place 
after  the  passage  of  the  wave.  In  fact,  from  whatever  side  we 
examine  this  theory,  it  presents  nothing  but  difficulties,  of 
which  only  a  few  have  here  been  suggested. 

Another  theory  of  mountain  formation,  which  was  first  in- 
tended to  be  applied  to  the  Appalachian  chain,  but  which  has 
since  been  stretched  to  fit  all  mountain  ranges,  is  that  of  Pro- 
fessor James  Hall,  which  has  also  been  supported  by  Mr.  Sterry 
Hunt,  and  by  Mr.  Yose,  in  a  work  entitled  u  Orographic  Ge- 
ology." This  last-named  gentleman,  who  prints  "  civil  engi- 
neer" after  his  name  on  the  title-page  of  his  work,  as  if  he 
feared  that,  by  some  possibility,  he  should  be  taken  for  a  geol- 
ogist, has  adopted  Mr.  Hall's  theories  in  toto,  which  he  could 
more  easily  do,  since  he  was  not  hampered  by  any  of  those 
difficulties  which  have  their  origin  in  a  personal  acquaintance 
with  the  subject. 

Professor  Hall's  theory  is  rather  an  application  or  enlarge- 
ment of  the  views  of  Herschel  and  Babbage  in  regard  to  the 
manner  in  which  the  internal  heat  of  the  earth  may  be  sup- 
posed to  affect  regions  where  deposition  or  denudation  of  the 
strata  are  taking  place.  As  it  is  known  from  observation  that 
the  isogeothermal  lines,  as  they  are  called,  that  is,  the  lines  of 
equal  temperature  beneath  the  surface  of  the  earth,  rise  and 
fall  with  the  elevations  and  depressions  of  the  surface,  so  that 


100  Vblcanism  and  Mountain-Building. 

the  underground  isothermal  surfaces  correspond  in  contour 
with  the  external  surface.  This  being  the  case,  if  over  a  cer- 
tain region  there  is  a  deposition  of  sediment  going  on,  then 
there  must  be  a  rising  of  the  temperature  beneath  while  the 
isogeothermals  are  adapting  themselves  to  the  new  surface. 
Exactly  the  opposite  will  take  place  in  a  region  from  which  the 
material  is  being  abraded.  Thus,  as  erosion  and  deposition  of 
sediments  are  always  going  on,  there  are  always  changes  of  tem- 
perature taking  place  over  the  earth's  surface,  by  which  expan- 
sion and  contraction  of  the  rocks  are  effected.  This  is  pre- 
sumed by  Babbage  to  be  an  agency  of  the  first  importance  in 
producing  geological  changes,  and  Herschel  also  insists  upon 
the  increase  and  relief  of  pressure  in  different  regions,  accord- 
ing as  material  is  deposited  or  abraded,  as  also  necessarily 
being  one  of  the  mightiest  of  the  causes  by  which  changes  in 
the  configuration  of  the  surface  are  brought  about. 

These  views  have  been  applied  by  Professor  Hall  in  this  way. 
Deposition  of  sedimentary  materials  can  only  take  place  con- 
tinuously and  for  a  long  time  in  a  region  which  is  subsiding,  as 
all  geologists  will  readily  admit,  since  detritus  must  be  car- 
ried from  a  higher  to  a  lower  region,  and  if  that  less  elevated 
area  does  not  subside  it  will  soon  be  filled  up  with  sediment. 
Subsidence,  however,  according  to  Professor  Hall,  involves  pli- 
cation or  folding  of  the  strata,  which  must  take  place  when 
large  thicknesses  of  material  are  pressed  downwards.  To  use 
the  Professor's  own  words  :  "  By  this  process  of  subsidence,  as 
the  lower  side  becomes  gradually  curved,  there  must  follow,  as 
a  consequence,  rents  and  fractures  upon  that  side ;  or  the  di- 
minished width  of  surface  above,  caused  by  this  curving  below, 
will  produce  wrinkles  and  foldings  of  the  strata."  Further  on 
he  adds :  "  But  the  folding  of  the  strata  seems  to  me  a  very 
natural  and  inevitable  consequence  of  the  process  of  subsi- 
dence." The  results  are,  according  to  this  theory,  that  moun- 
tain chains  do  not  occur  except  where  there  is  a  great  thick- 
ness of  sedimentary  deposits,  and  that  these  become  plicated  by 
their  own  subsidence.  Hence  plication  is  characteristic  of  all 
mountain  chains  ;  so,  also,  is  metamorphism,  for  in  the  subsi- 
dence the  material  has  been  brought  into  such  relations  of 
position  as  to  cause  the  isothermal  planes  to  ascend  into  it, 


Vblcanism  and  Mountain-Building.  101 

and  thus  to  bring  it  into  such  conditions  of  temperature  as  to 
facilitate  those  chemical  changes  which  result  in  converting  a 
sedimentary  into  a  metamorphic  rock.    Hence,  also,  a  synclinal 
structure  and  an  axis  of  metamorphic  rocks  are  to  be  expected 
in  every  great  mountain  chain.     But  how  the  mountain  chain  j 
is  obtained  from  the  depressed  mass  of  strata  is  nowhere  ex-J  ^ 
plained  by  the  author  of  the  theory  in  question ;  hence  it  hasv 
been  aptly  characterized  by  Professor  Dana  as  "  a  theory  for^ 
the  origin  of  mountains,  with  the  origin  of  mountains  left  out."  ; 
Indeed,  there  is  no  point  in  which  it  will  stand  the  test  of 
examination.     It  admits  of  mathematical  demonstration  that  7 
the  assigned  cause  would  not  be  sufficient  to  cause  the  plication. 
This  can  also  be  made  apparent  to  the  eye  by  drawing  a  dia- 
gram representing  a  section  of  a  portion  of  the  earth's  crust  on 
a  natural  scale,  laying  off  an  area  of  subsidence  with  an  amount 
of  depression  equivalent  to  the  assumed  thickness  of  the  strati- 
fied rocks,  say  of  the  Appalachian  chain,  and  observing  the  rela- 
tive length  of  the  lines  representing  the  original  surface  and 
that  of  the  depressed  mass.     The  result  will  be  quite  conclu- 
sive as  to  the  plication  of  strata  from  their  own  subsidence, 
except  where  that  subsidence  is  extremely  local.     Neither  is  it 
true  that  mountain  ranges  exhibit  usually  anything  like  the 
kind  of  synclinal  structure  required  by  Professor  Hall's  theory  ; 
indeed,  if  we  can  understand  what  this  structure  would  be  most 
likely  to  be,  there  is  no  such  chain  anywhere.     The  theory,  as 
set  forth  by  its  author,  is  left  in  such  a  vague  form  that  it  seems 
impossible  to  bring  it  to  any  crucial  test,  and  one  has  to  be 
content  with  finding  in  it  nothing  which  will  bear  examination. 

It  must  be  borne  in  mind  also,  in  this  connection,  that  neither  > 
Babbage  nor  Herschel  were  geologists,  and  that,  consequently, 
their  views  with  regard  to  the  relative  importance  of  different 
geological  agents  or  conditions  are  not  to  be  accepted  without 
careful  investigation.  A  little  consideration  will  show  that 
although  there  may  be  something  plausible,  and  even  attrac- 
tive, about  these  theories  of  metamorphism  and  change  of 
relief  of  the  surface  in  consequence  of  denudation  and  the 
accumulation  of  sediments,  the  facts  are  far  from  supporting 
them,  at  least  to  anything  like  the  extent  assumed  by  Professor 
Hall.  If  the  earth's  crust  is  so  sensitive  to  pressure  that  it  is 
8 


102  Vblcanism  and  Mountain-Building. 

ready  to  respond  to  the  very  gradual  and  comparatively  slight 
difference  of  level  resulting  from  abrasion  of  the  rock  at  one 
locality  and  removal  of  the  detritus  thus  formed  to  another, 
how  is  it  that  the  weight  of  the  great  mountain  masses  is  sup- 
-V  K  ported,  or  how  could  they  have  originated  at  all  ?  It  is  not 
possible  to  conceive  that,  during  all  the  preceding  stages  of 
the  earth's  existence,  its  interior  should  be  so  insensible  to 
the  pressure  of  the  crust  as  to  allow  ranges  like  the  Alps, 
the  Andes,  and  the  Himalayas  to  be  built  upon  it,  and  that,  at 
the  present  epoch,  it  has,  all  at 'once,  assumed  such  a  condition 
of  sensitiveness  as  to  respond  by  its  motion  to  any  transference 
\  of  weight  from  one  region  to  another.  It  would  not  be  diffi- 
cult to  suggest  other  valid  reasons  for  refusing  to  accept  Her- 
schel's  views ;  but  enough  has  been  said  to  indicate  clearly 
that  they  are  not  admissible  as  a  basis  for  orographic  general- 
izations. The  ideas  of  Babbage  in  regard  to  the  rise  of  the 
isogeothermal  planes  in  consequence  of  the  accumulation  of 
sediments  are  more  philosophical  than  those  of  Herschel ;  but 
the  facts  do  not  bear  us  out  in  inferring  that  extensive  meta- 
morphism  will  necessarily  be  the  result  of  the  resulting  in- 
crease of  temperature.  An  examination  of  a  section  of  strati- 
fied rocks  piled  upon  each  other  to  a  height  of  several  thousand 
feet,  resting  horizontally  on  the  granite,  and  quite  unaltered  as 
to  texture  since  deposition,  is  sufficient  evidence  that  heavy  ac- 
cumulations of  sediment  are  not  necessarily  rendered  crystal- 
line by  the  rise  of  the  isogeothermal  planes  ;  but  that  some- 
thing else  is  required  to  bring  about  that  complex  series  of 
chemical  changes  which  we  designate  by  the  term  "  metamor- 
phic  action."  Such  sections  as  those  alluded  to  here  may  be 
seen  in  abundance  over  a  wide  area  in  the  Rocky  Mountains, 
and  along  the  Colorado  and  its  tributaries,  as  well  as  elsewhere. 
Indeed,  the  Appalachians  and  the  Juras  themselves  show  that 
great  masses  of  rock  may  be  piled  up,  and  even  extensively 
plicated,  with  but  little  resulting  metamorphism. 

The  gist  of  Professor  Hall's  theory  seems  to  be,  that  moun- 
tains are  logically  connected  with  large  deposits  of  sedimentary 
rocks ;  and  this  is  true,  but  exactly  in  the  opposite  way  from 

(that  imagined  by  him.     The  sedimentary  beds  are  thick  be- 
cause the  mountains  pre-existed  from  the  destruction  of  which 


Volcanism  and  Mountain- Building.  103 

they  could  be  formed  ;  not  that,  having  been  already  formed,  \  . 
they  were  afterwards  made  into  mountains.  There  can  be  no'' 
formation  of  detrital  or  sedimentary  deposits,  that  is,  of  strati- 
fied rocks,  without  the  previous  existence  of  some  higher  region 
from  which  the  material  can  be  derived.  Hence,  if  the  com- 
bined thickness  of  the  sedimentary  beds  about  a  great  moun- 
tain centre  reaches  a  high  figure,  it  is  simply  because  the  con- 
ditions for  the  accumulation  of  such  beds  have  been  favorable. 
With  a  surface  entirely  flat,  the  amount  of  deposition  must 
necessarily  be  very  small  and  almost  entirely  confined  to  such 
materials  as  are  produced  by  chemical  or  organic  action.  But 
those  beds  which  are  chemically  precipitated  or  formed  by  living 
organisms  are  vastly  inferior  in  thickness  to  those  which  result 
from  the  piling  up  of  detrital  materials,  or  such  as  are  abraded 
from  previously  existing  rocks  through  the  agency  of  water. 

It  is  evident  that,  in  theorizing  in  regard  to  mountain-making 
and  deposition  of  sediments,  too  little  regard  has  been  had  to 
the  origin  of  these  sediments.  The  fact  is  ignored  that  all 
the  sedimentary  formations  must  have  been  originally  derived 
from  the  original  crust  of  the  earth  as  it  existed  after  cooling 
had  gone  so  far  that  water  had  begun  to  condense  upon  its  sur- 
face ;  they  must  have  had  some  higher  region  from  which  to  be 
swept  downwards.  These  higher  regions  were,  in  the  first 
place,  evidently  the  ridges  or  wrinkles  of  the  granitic  and  gneis- 
soid  crust  raised  above  the  general  level  by  the  first  efforts  of 
the  consolidated  crust  to  adapt  itself  to  the  interior.  The  de- 
tritus thus  carried  down  the  flanks  of  the  ridges  was,  early  in 
the  geological  history  of  the  earth,  mostly  deposited  in  the 
ocean,  which  must  originally  have  covered  even  a  larger  por- 
tion of  our  surface  than  it  now  does.  Hence  the  predominance, 
or  almost  exclusive  existence,  of  marine  formations,  during  the 
earlier  geological  ages.  It  was  not  until  a  large  body  of  sedi- ' 
mentary  deposits  had  thus  been  formed,  and  these  masses  had 
begun  to  be  themselves  raised  above  the  sea-level,  that  their 
abrasion  could  furnish  material  for  a  set  of  beds  not  derived 
from  the  original  crust.  And  this  process  having  once  been' 
gone  through,  the  same  thing  may  have  been  repeated  again 
and  again.  How  many  times  such  a  destruction  of  pre-existing 
sediments  and  formations  of  new  deposits  from  the  ruins  may 


104  Volcanism  and  Mountain-Building. 

have  taken  place  in  any  one  region,  we  cannot  say ;  but  we 
have  no  reason  for  assuming  that  all  over  the  world  this  has 
gone  on  to  such  an  extent  that  none  of  the  original  crust  can 
be  anywhere  visible. 

The  area  of  the  continental  masses  gradually  and  constantly 
expanding,  and  the  depth  of  the  oceanic  basins  increasing, 
strata  formed  by  fluviatile  action  began  to  be  deposited,  and  of 
course  contained  the  remains  of  fresh-water  and  land  animals. 
If,  then,  no  new  axis  of  elevation  was  originated,  and  there  was 
no  further  rise  of  the  land,  the  formation  of  new  stratified  de- 
posits would  eventually  reach  its  limit,  because  the  newly 
formed  beds  would  have  risen  to  the  level  of  the  highest  exist- 
ing land,  and,  equilibrium  of  the  surface  having  been  restored, 
there  could  be  no  more  erosion,  except  on  the  smallest  scale. 
Thus,  in  many  mountain  chains,  as  already  noticed,  there  has 
been  a  cessation  of  growth  at  an  early  period ;  while  in  others 
—  and  these  are  the  great  chains  of  the  world  —  growth  has 
continued  down  even  to  the  very  latest  epoch.  In  these  in- 

f  stances  of  continued  growth  there  has  usually  been  a  tendency 
to  the  formation  of  a  new  axis  or  uplift  parallel  with  the  earlier 
one,  and  at  no  great  distance  from  it,  on  one  side  or  the  other. 
Thus  opportunity  has  been  given  for  the  processes  of  abrasion 
and  reconstruction  of  strata,  and  the  mountain  mass  has 
developed  itself,  until  we  have,  as  the  final  result,  a  series  of 
approximately  parallel  ranges,  showing  in  their  structure  the 
complicated  nature  of  the  processes  by  which  they  have  been 
formed. 

This  method  of  growth  by  lateral  aggregation  is  most  admi- 
rably exemplified  in  the  Cordilleras  of  North  America.  In  this 
complex  of  chains,  we  have,  first,  the  granitic  and  gneissic 

^nucleus  or  basis,  which  is  the  floor  on  which  all  the  stratified 
formations  have  been  laid  down,  and  from  whose  ruins  the  bulk 
of  the  materials  have  come  for  building  up  the  ranges.  This 
ancient  nucleus  is,  in  places,  low  down  and  concealed  by  heavy 
masses  of  stratified  formations ;  in  other  regions  raised  into 

^lofty^crests,  possibly  the  highest  of  the  whole  series.  The 
stratified  deposits,  which  have  been  formed  from  this  nucleus, 
have  been,  from  time  to  time,  folded,  upheaved,  and  invaded 
by  eruptive  rocks,  whose  distribution,  however,  has  been  very 
irregular. 


Volcanism  and  Mountain-Building.  105 

Oil  the  western  or  oceanic  side  the  disturbances  have  been 
most  extensive.  Here  the  upturnings  and  crushings  of  the 
strata  have  taken  place  on  the  grandest  scale,  and  new  axes 
of  elevation  have  been  formed  at  successive  geological  epochs, 
the  close  of  the  Jurassic  and  of  the  Miocene  tertiary  being 
two  of  the  most  important  of  these.  On  the  eastern  or  Rocky- 
Mountain  side  no  great  folding  or  metamorphism  of  the  rocks 
occurred  after  the  close  of  the  Azoic  period  ;  but  a  gradual 
elevation  of  the  whole  mass  of  strata  took  place,  the  larger 
portion  of  which  was  during  the  Tertiary  epoch.  By  this  uplift 
the  unaltered  cretaceous  rocks  were  raised  to  an  elevation  in  f 
places  greater  than  ten  thousand  feet  above  the  present  sea-level.  \  ^ 
This  rise  of  the  land  continued  until  the  most  recent  geologi- 
cal times,  or  almost  down  to  the  present  day ;  but  how  much 
of  the  difference  in  elevation  between  the  land  and  sea  is  due 
to  actual  positive  uplift,  and  how  much  to  a  sinking  of  the 
ocean,  we  have  at  present  scarcely  any  means  of  judging.  At 
all  events  there  were,  on  this  side  of  the  Cordilleras,  almost 
no  local  disturbances  or  foldings  of  the  sedimentary  rocks, 
which  still  lie  upon  each  other  in  regular  sequence,  dipping  at 
a  low  angle  from  the  central  crystalline  masses  everywhere, 
except  just  at  the  line  of  junction  of  the  two  formations,  where, 
for  a  distance  of  a  few  thousand  feet  at  right  angles  to  their 
trend,  the  stratified  formations,  from  Silurian  to  Carboniferous, 
are  turned  up  on  edge  in  the  most  wonderful  manner,  and 
sometimes  completely  overthrown,  so  as  to  dip  towards  the 
mountains,  but  not  metamorphosed  or  rendered  crystalline  in 
structure.  Neither  were  these  disturbances  attended,  to  any 
considerable  extent,  by  outbursts  of  volcanic  or  eruptive  mate- 
rial ;  while  on  the  western  side  of  the  continent  these  occurred 
on  the  grandest  scale. 

An  examination  of  all  that  has  been  published  with  regard 
to  the  geology  of  the  Andes  indicates  that  when  this  mighty 
chain  of  mountains  comes  to  be  thoroughly  studied,  there  will 
be  many  analogies  discovered  between  them  and  the  North 
American  Cordilleras.  Some  such  could  already  be  indicated 
if  space  permitted  ;  but,  as  yet,  no  careful  section  has  ever  been 
made  across  the  South  American  ranges  by  any  trained  strati- 
graphical  geologist. 


106  Volcanism  and  Mountain-Building. 

In  the  case  of  the  Appalachians,  we  have  to  do  with  a  chain 
of  mountains  which  has  no  crystalline  centre  or  axis,  and 
.  which  consists,  at  least  through  a  great  portion  of  its  length, 
of  a  pile  of  detrital  materials,  distinctly  stratified,  all  belong- 
ing to  the  Paleozoic  epoch,  scantily  provided  with  fossils,  but 
separable  into  a  number  of  well-marked  groups  by  the  aid  of 
lithological  characters.  These  groups  have  much  their  great- 
est development  towards  the  northeast  and  southwest,  and 
they  dip  in  general  towards  the  west  or  northwest,  so  that  in 
going  in  that  direction  we  rise  on  to  more  recent  strata.  Pro- 
ceeding westerly,  moreover,  we  find  the  plications,  which  are 
well  marked  on  the  eastern  edge  of  the  chain,  gradually  dis- 
appearing ;  while  at  the  same  time  the  groups  of  strata  are 
found  to  be  made  up  of  finer  materials  and  to  be  gradually 
thinning  out,  thus  indicating  a  greater  distance  from  the 
source  from  which  the  detritus  of  which  they  are  made  up 
was  derived.  Hence  we  can  hardly  fail  to  draw  the  inference 
that  this  source  was  somewhere  to  the  east  of  the  range,  and 
that  the  region  from  which  the  plicating  force  proceeded  is 
also  to  be  sought  for  on  that  side.  If  this  be  the  case,  then  it 
seems  probable  that  there  must  have  been  a  high  range  of 
crystalline  rocks  on  the  eastern  borders  of  the  Appalachians,  for 
there  is  no  other  conceivable  source  of  supply  which  would 
satisfy  the  required  conditions.  The  detritus  of  which  the 
rocks  of  this  range  are  made  up  came  then  from  a  higher 
region,  which  has  since  disappeared.  It  must  have  subsided, 
and  this  subsidence  was,  as  we  conceive,  the  cause  of  the  plica- 
tion of  the  beds  which  had  been  formed  on  its  western  slopes, 
these  beds  having  been  elevated  and  crumpled  or  flexed  as 
the  mass  exterior  to  them  was  gradually  sinking. 

Subsidence,  then,  we  regard  as  the  chief  cause  of  the  plica- 
tion of  strata ;  but  it  is  not  the  sinking  of  the  stratified  mass 
itself  which  is  the  principal  effective  agent  in  bringing  about 
its  folding.  There  can  be  no  plication,  to  any  appreciable  ex- 
tent, without  an  actual  shortening  of  the  plicated  strata,  and 
this  can  only  come  from  a  lateral  thrust,  such  as  would  be 
exerted  by  a  subsiding  mass  upon  a  region  exterior  to  it. 
Hence  if  we  find  the  newer  strata  on  the  flanks  of  an  older 
central  nucleus  compressed  together  by  folding,  we  are  jus- 


Vblcanism  and  Mountain-Building.  107 

tified  in  presuming  that  it  is  the  subsidence  of  the  latter  which 
has  given  rise  to  the  plication  of  the  adjacent  lower  region. 
If  the  subsiding  higher  area  be  of  comparatively  large  dimen- 
sions, there  will  be  a  tendency  to  produce  elevation  to  a  certain 
extent  on  each  side. 

The  folding  of  the  newer  strata  along  the  base  of  the  Alps, 
and  of  the  Jura  even,  has  repeatedly  been  explained  by  suc- 
cessive upheavals. of  the  Alpine  masses;  indeed,  these  have  been 
taken  for  granted  by  most  geologists,  without  any  attempt  to 
investigate  the  manner  in  which  the  assumed  cause  could 
bring  about  any  such  result.  It  is  certainly  clear  enough  that 
elevation  of  the  central  mass  would  produce  a  lengthening 
rather  than  a  shortening  of  the  base  on  which  rest  the  strata 
which  are  uplifted,  and  that  this  is  something  quite  the  opposite 
of  what  is  required  to  cause  plication.  From  a  careful  study 
of  the  stratigraphical  geology  of  the  Sub-Himalayan  ranges, 
Mr.  Medlicott,  of  the  India  Survey,  was  led  to  the  conclusion 
that  the  peculiar  position  of  the  rocks  of  which  those  moun- 
tains are  made  up  could  only  be  accounted  for  on  the  theory 
of  a  subsidence  of  the  central  mass,  and  the  same  idea  has 
been  applied  by  him  to  explain  the  contortions  of  the  tertiary 
beds  on  the  flanks  of  the  Alps,  as  well  as  to  plications  of 
stratified  rocks  in  general.*  And  so  far  as  this  geologist  has 
developed  his  ideas  on  this  subject,  they  are  identical  with 
those  formed  by  us  in  studying  the  mountain  systems  of  North 
America. 

We  have  thus  endeavored  to  give  an  idea  of  the  progress 
making  by  geologists  in  getting  towards  a  solution  of  some  of 
the  principal  problems  of  orography.  The  subject  is  a  very 
comprehensive  and  difficult  one,  and  it  is  far  from  easy  to 
treat  it  in  a  popular  manner.  It  is  evident  that  much  remains 
to  be  done  in  this  line  of  research,  and  that  it  is  desirable 
that  chemists  and  physicists  should  lend  a  helping  hand  ;  but 
the  burden  of  the  work  must  fall  on  the  geologists,  and  one 
important  step  will  have  been  made  when  it  is  clearly  recog- 
nized that  geological  facts  must  be  allowed  to  have  more 
weight  than  chemical  theories,  and  that  a  large  experience  in 
the  field  is  a  necessary  prerequisite  to  valuable  theorizing. 

L    *  See  Quarterly  Journal  of/#g^61t%ifc3l>dfeiej;y  of  London,  XXIV.  34. 

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